Added GRPC code generator to flatc.

Also added simple (in-process) test.

Change-Id: I38580d554dd52f590e3396ec4846e07546dcf07d
Tested: on Linux.

docs/source/Compiler.md

@@ -33,6 +33,8 @@ For any schema input files, one or more generators can be specified:
 
 -   `--php`: Generate PHP code.
 
+-   `--grpc`: Generate RPC stub code for GRPC.
+
 For any data input files:
 
 -   `--binary`, `-b` : If data is contained in this file, generate a

docs/source/Schemas.md

@@ -237,7 +237,8 @@ as the response (both of which must be table types):
     }
 
 What code this produces and how it is used depends on language and RPC system
-used, FlatBuffers itself does not offer this functionality.
+used, there is preliminary support for GRPC through the `--grpc` code generator,
+see `grpc/tests` for an example.
 
 ### Comments & documentation