C# bindings (#650)

* First workin version of the C# bindings

* Update README.md

Signed-off-by: mvenditto <venditto.matteo@gmail.com>

* Added more docs + fixed prompt callback signature

* build scripts revision

* Added .editorconfig + fixed style issues

---------

Signed-off-by: mvenditto <venditto.matteo@gmail.com>

gpt4all-bindings/csharp/build_win-mingw.ps1

@@ -0,0 +1,17 @@
+$ROOT_DIR = '.\runtimes\win-x64'
+$BUILD_DIR = '.\runtimes\win-x64\build\mingw'
+$LIBS_DIR = '.\runtimes\win-x64\native'
+
+# cleanup env
+Remove-Item -Force -Recurse $ROOT_DIR -ErrorAction SilentlyContinue | Out-Null
+mkdir $BUILD_DIR | Out-Null
+mkdir $LIBS_DIR  | Out-Null
+
+# build
+cmake -G "MinGW Makefiles" -S ..\..\gpt4all-backend -B $BUILD_DIR
+cmake --build $BUILD_DIR --parallel --config Release
+
+# copy native dlls
+cp "C:\ProgramData\chocolatey\lib\mingw\tools\install\mingw64\bin\*dll" $LIBS_DIR
+cp "$BUILD_DIR\libllmodel.dll" $LIBS_DIR
+cp "$BUILD_DIR\bin\libllama.dll" $LIBS_DIR