Apache PIG - Move grunt from javacc to ANTLR

by Dilip for Apache Software Foundation

The project is more on the lines of moving gruntparser to queryparser. Currently, the parser for queries is in ANTLR, but Grunt is still javacc. The parser is very difficult to work with, and next to impossible to understand or modify. ANTLR provides a much cleaner, more standard way to generate parsers/lexers/ASTs/etc, and moving from javacc to Grunt would be huge as we continue to add features to Pig.