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/Gpt4All/GenLLModelBindings.rsp

@@ -0,0 +1,21 @@
+--config
+exclude-funcs-with-body
+--with-access-specifier
+*=Public
+--include-directory
+..\..\..\gpt4all-backend\
+--file
+..\..\..\gpt4all-backend\llmodel_c.h
+--libraryPath
+libllmodel
+--remap
+sbyte*=IntPtr
+void*=IntPtr
+--namespace
+Gpt4All.Bindings
+--methodClassName
+NativeMethods
+--output
+.\Bindings\NativeMethods.cs
+--output-mode
+CSharp