missing lexer rules if tokenVocab defined

Fix is due to a problem I encountered, see http://stackoverflow.com/questions/22285912/antlr-v3-token-file-array-and-null

Problem was: lexer rules for tokens defined in the tokenVocab where not generated which resulted in NullPointerExceptions in the lexer.

This pull request fixes this issue (and I have fixed some broken links in the README.txt). The reasons why I want to use a tokenVocab already in the parser are explained in the StackOverflow thread