Further grammar.md fixes: union types, idents, string constants.
Further grammar.md fixes: union types, idents, string constants.

Change-Id: I51db0511c52c79f2b322a1fdef798b061941887b

google/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,google/flatbuffers,chenkai036/flatbuffers,chenkai036/flatbuffers,endorph-soft/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,pjulien/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,rw/flatbuffers,DavadDi/flatbuffers,alexames/flatbuffers,hgl888/flatbuffers,DavadDi/flatbuffers,DavadDi/flatbuffers,google/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,chenkai036/flatbuffers,hgl888/flatbuffers,endorph-soft/flatbuffers,rw/flatbuffers,evolutional/flatbuffers,hgl888/flatbuffers,royalharsh/flatbuffers,google/flatbuffers,stewartmiles/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,endorph-soft/flatbuffers,pjulien/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,hgl888/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,stewartmiles/flatbuffers,evolutional/flatbuffers,chenkai036/flatbuffers,evolutional/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,rw/flatbuffers,stewartmiles/flatbuffers,stewartmiles/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,alexames/flatbuffers,alexames/flatbuffers,pjulien/flatbuffers,google/flatbuffers,alexames/flatbuffers,evolutional/flatbuffers,chenkai036/flatbuffers,evolutional/flatbuffers,DavadDi/flatbuffers,DavadDi/flatbuffers,royalharsh/flatbuffers,royalharsh/flatbuffers,endorph-soft/flatbuffers,pjulien/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,rw/flatbuffers,endorph-soft/flatbuffers,rw/flatbuffers,hgl888/flatbuffers,alexames/flatbuffers,rw/flatbuffers,royalharsh/flatbuffers,hgl888/flatbuffers,pjulien/flatbuffers,rw/flatbuffers,evolutional/flatbuffers,chenkai036/flatbuffers,pjulien/flatbuffers,rw/flatbuffers,evolutional/flatbuffers,evolutional/flatbuffers,royalharsh/flatbuffers,google/flatbuffers,rw/flatbuffers,pjulien/flatbuffers,evolutional/flatbuffers,alexames/flatbuffers,chenkai036/flatbuffers,alexames/flatbuffers,chenkai036/flatbuffers,royalharsh/flatbuffers,endorph-soft/flatbuffers,endorph-soft/flatbuffers,google/flatbuffers,DavadDi/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,google/flatbuffers,google/flatbuffers,rw/flatbuffers,evolutional/flatbuffers,endorph-soft/flatbuffers,google/flatbuffers,google/flatbuffers,alexames/flatbuffers,chenkai036/flatbuffers,royalharsh/flatbuffers,alexames/flatbuffers,stewartmiles/flatbuffers,google/flatbuffers,pjulien/flatbuffers,google/flatbuffers,pjulien/flatbuffers,stewartmiles/flatbuffers,chenkai036/flatbuffers,evolutional/flatbuffers,royalharsh/flatbuffers,stewartmiles/flatbuffers