Fixed some incorrect stb-image extern function decls.

modules/stb-image/stb-image.monkey2

@@ -15,8 +15,8 @@ Struct stbi_io_callbacks
 	Field eof:Int( Void Ptr )
 End
 
-Function stbi_load:UByte Ptr( filename:String,x:Int Ptr,y:Int Ptr,comp:Int Ptr,req_comp:Int )
-Function stbi_load_from_memory:UByte Ptr( buffer:UByte Ptr,x:Int Ptr,y:Int Ptr,comp:Int Ptr,req_comp:Int )
+Function stbi_load:UByte Ptr( filename:CString,x:Int Ptr,y:Int Ptr,comp:Int Ptr,req_comp:Int )
+Function stbi_load_from_memory:UByte Ptr( buffer:UByte Ptr,len:Int,x:Int Ptr,y:Int Ptr,comp:Int Ptr,req_comp:Int )
 Function stbi_load_from_callbacks:UByte Ptr( clbk:stbi_io_callbacks Ptr,user:Void Ptr,x:Int Ptr,y:Int Ptr,comp:Int Ptr,req_comp:Int )
 
 Function stbi_image_free( data:Void Ptr )