Ensure the token stream is always properly set for Grammar, GrammarRootAST, and LeftRecursiveRuleAnalyzer
Clean up imports
Add error 147: left recursive rule 'a' must contain an alternative which is not left recursive; fixes antlr/antlr4#140
Add error 148: left recursive rule 'a' contains a left recursive alternative which can be followed by the empty string
Updated error messages and documentation