Implemented list command.
Added RFC2822 which is needed to implement FETCH.
Lexer handles different types of unquoted strings

This fixes #17
Expands lexer tests for astring with closer attention to ABNF in spec
Merge pull request #18 from RossJHagan/lexer-tests-expanded

Expands lexer tests for astring with closer attention to ABNF in spec
Fixed some of the failing lexer tests.