ruby: drop NetworkMessage class

This patch drops the NetworkMessage class. The relevant data members and functions
have been moved to the Message class, which was the parent of NetworkMessage.

imported patch jason/slicc-external-structure-fix

slicc: have a central mechanism for creating a code_formatter.
This makes it easier to add global variables like protocol

slicc: Pure python implementation of slicc.
This is simply a translation of the C++ slicc into python with very minimal
reorganization of the code. The output can be verified as nearly identical
by doing a "diff -wBur".

Slicc can easily be run manually by using util/slicc