sdk: introduce Spice SDK (#676)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Adds a flat-C, headers-only library for writing DLL plugins with spice.

This is meant to be an alternative to writing applications over spice
API which doesn't suit some scenarios like writing custom
high-performance I/O modules.

All you have to do is:

1. Create a 32-bit or 64-bit DLL with `spice_sdk_entry_point` as a
DLLExport
1. Include `spicesdk.h`, and optionally `spicesdk_io.h` (see
`extras\sdk\include`)
1. `spice_sdk_entry_point` will be called when hooks get initialized.
Call `init` with valid parameters.
1. When `init` returns, `SPICE_SDK_V0` will be filled out with a series
of function pointers; your DLL can now start calling into it.
1. Compile your DLL and add it as a DLL hook (`-k`) in spice when
launching the game.

See `v0_cpp.cpp` for an example.

V0 implements the following functions:

```
    log;

    get_game_info;
    get_avs_info;

    get_button;
    set_button;

    get_analog;
    set_analog;

    get_light;
    set_light;

    set_touch;
    clear_touch;

    insert_card;
    set_keypad;
```

V0 is focused on providing common utility functions needed in a lot of
DLL hooks (get AVS info, log messages to file), and implementing I/O.

In the future, we could have more interesting things like:

* scanning and modifying memory 
* installing DLL hooks
* having direct hooks into I/O emulation modules
* getting full tape LEDs
* having a callback into DX9 `Present` call
* drawing an ImGui window

More detailed documentation is coming soon in form of a wiki page.

## Testing
See included sample DLL.

src/spice2x/build_all.sh

@@ -68,8 +68,8 @@ DIST_FOLDER="./dist"
 DIST_NAME="spice2x-$(date +%y)-$(date +%m)-$(date +%d).zip"
 DIST_NAME_EXTRAS="spice2x-$(date +%y)-$(date +%m)-$(date +%d)-full.zip"
 DIST_COMMENT=${DIST_NAME}$'\n'"$GIT_BRANCH - $GIT_HEAD"$'\nThank you for playing.'
-TARGETS_32="spicetools_stubs_kbt spicetools_stubs_kld spicetools_cfg spicetools_cfg_linux spicetools_spice spicetools_spice_laa spicetools_spice_linux spicetools_stubs_cpusbxpkm"
-TARGETS_64="spicetools_stubs_kbt64 spicetools_stubs_kld64 spicetools_stubs_nvEncodeAPI64 spicetools_stubs_nvcuvid spicetools_stubs_nvcuda spicetools_spice64 spicetools_spice64_linux"
+TARGETS_32="spicetools_stubs_kbt spicetools_stubs_kld spicetools_cfg spicetools_cfg_linux spicetools_spice spicetools_spice_laa spicetools_spice_linux spicetools_stubs_cpusbxpkm spicetools_sdk_sample_v0_flat_c_32"
+TARGETS_64="spicetools_stubs_kbt64 spicetools_stubs_kld64 spicetools_stubs_nvEncodeAPI64 spicetools_stubs_nvcuvid spicetools_stubs_nvcuda spicetools_spice64 spicetools_spice64_linux spicetools_sdk_sample_v0_flat_c_64 spicetools_sdk_sample_v0_cpp_64"
 TARGETS_XP32="spicetools_cfg spicetools_spice"
 TARGETS_XP64="spicetools_spice64"
 
@@ -269,6 +269,8 @@ rm -rf ${OUTDIR_EXTRAS}
 mkdir -p ${OUTDIR_EXTRAS}
 mkdir -p ${OUTDIR_EXTRAS}/largeaddressaware
 mkdir -p ${OUTDIR_EXTRAS}/linux
+mkdir -p ${OUTDIR_EXTRAS}/sdk/samples/32
+mkdir -p ${OUTDIR_EXTRAS}/sdk/samples/64
 if ((BUILD_XP > 0))
 then
 mkdir -p ${OUTDIR_EXTRAS}/winxp
@@ -281,16 +283,8 @@ then
     cp ${BUILDDIR_32}/spicetools/spicecfg-pdb.pdb ${OUTDIR} 2>/dev/null
     cp ${BUILDDIR_32}/spicetools/32/spice-pdb.exe ${OUTDIR} 2>/dev/null
     cp ${BUILDDIR_32}/spicetools/32/spice-pdb.pdb ${OUTDIR} 2>/dev/null
-    #cp ${BUILDDIR_32}/spicetools/32/kbt.dll ${OUTDIR}/stubs/32 2>/dev/null
-    #cp ${BUILDDIR_32}/spicetools/32/kld.dll ${OUTDIR}/stubs/32 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/spice64-pdb.exe ${OUTDIR} 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/spice64-pdb.pdb ${OUTDIR} 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/kbt.dll ${OUTDIR}/stubs/64 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/kld.dll ${OUTDIR}/stubs/64 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/nvEncodeAPI64.dll ${OUTDIR}/stubs/64 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/nvcuda.dll ${OUTDIR}/stubs/64 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/nvcuvid.dll ${OUTDIR}/stubs/64 2>/dev/null
-	#cp ${BUILDDIR_32}/spicetools/32/cpusbxpkm.dll ${OUTDIR}/stubs/32 2>/dev/null
 else
     # release files
     cp ${BUILDDIR_32}/spicetools/spicecfg.exe ${OUTDIR} 2>/dev/null
@@ -298,16 +292,15 @@ else
     cp ${BUILDDIR_32}/spicetools/32/spice.exe ${OUTDIR} 2>/dev/null
     cp ${BUILDDIR_32}/spicetools/32/spice_laa.exe ${OUTDIR_EXTRAS}/largeaddressaware/spice.exe 2>/dev/null
     cp ${BUILDDIR_32}/spicetools/32/spice_linux.exe ${OUTDIR_EXTRAS}/linux/spice.exe 2>/dev/null
-    #cp ${BUILDDIR_32}/spicetools/32/kbt.dll ${OUTDIR}/stubs/32 2>/dev/null
-    #cp ${BUILDDIR_32}/spicetools/32/kld.dll ${OUTDIR}/stubs/32 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/spice64.exe ${OUTDIR} 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/spice64_linux.exe ${OUTDIR_EXTRAS}/linux/spice64.exe 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/kbt.dll ${OUTDIR}/stubs/64 2>/dev/null
-    #cp ${BUILDDIR_64}/spicetools/64/kld.dll ${OUTDIR}/stubs/64 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/nvEncodeAPI64.dll ${OUTDIR}/stubs/64 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/nvcuda.dll ${OUTDIR}/stubs/64 2>/dev/null
     cp ${BUILDDIR_64}/spicetools/64/nvcuvid.dll ${OUTDIR}/stubs/64 2>/dev/null
     cp ${BUILDDIR_32}/spicetools/32/cpusbxpkm.dll ${OUTDIR}/stubs/32 2>/dev/null
+	cp ${BUILDDIR_32}/spicetools/32/sdk_sample_v0_flat_c.dll ${OUTDIR_EXTRAS}/sdk/samples/32/v0_flat_c.dll 2>/dev/null
+	cp ${BUILDDIR_64}/spicetools/64/sdk_sample_v0_flat_c.dll ${OUTDIR_EXTRAS}/sdk/samples/64/v0_flat_c.dll 2>/dev/null
+	cp ${BUILDDIR_64}/spicetools/64/sdk_sample_v0_cpp.dll ${OUTDIR_EXTRAS}/sdk/samples/64/v0_cpp.dll 2>/dev/null
 	if ((BUILD_XP > 0))
 	then
 		cp ${BUILDDIR_WINXP_32}/spicetools/spicecfg.exe ${OUTDIR_EXTRAS}/winxp 2>/dev/null
@@ -326,6 +319,9 @@ then
 		echo "WARNING: Couldn't get git to create the archive. Is this a git repository?"
 fi
 
+# sdk headers
+cp -r ./sdk/include ${OUTDIR_EXTRAS}/sdk
+
 # copy resources
 rm -rf ${OUTDIR_EXTRAS}/api
 mkdir ${OUTDIR_EXTRAS}/api