.gitignore compiled rfc grammar files
Gruntfile.js: add allowedStartRules to rfc parser
Gruntfile.js: register 'rfc' task
Grammar: rfc3261.pegjs - uncomment rules redefined in other files
Grammar: rfc3261.pegjs - fix literal underscores back to hyphens
Grammar: add actions/rfc3261.pegjs and .gitignore/grunt changes