Added AST::Expression object for complete expression statement
Cucumber plumbing for lexer and parser features file
Modified to require only ruby file (*.rb) to avoid errors while loading temp files *.rb~ created by  emacs
Updated colorprinter with print statements instaed of puts to eliminate newlines at the end
Added non-destructive look behind method to traverse back to a previous token in lexer
:Updated parser statement and other code
Updated parser lexer and test code