Functional configuration refactoring. Fixes #5

Inspired by @davecheney post: http://dave.cheney.net/2014/10/17/functional-options-for-friendly-apis
Merge pull request #7 from xarg/master

Functional configuration refactoring. Fixes #5
#1 developing test suite. Added tests for CAPABILITY and LOGOUT. Other commands TODO.
#1 developing test suite. Added tests for CAPABILITY and LOGOUT. Other commands TODO.
transform the lexer.skipSpace to skype only one space and handle the issue #6 / add of astring exception to the astring bytes check
Removed support for multiple mailstores. Fixes #13
Merge pull request #15 from xarg/master

Removed support for multiple mailstores. Fixes #13
Check for empty ASTRING in lexer.

Also updated README to show valid command tags. It was the invalid
command tags in the README that exposed the empty ASTRING problem.
Adds basic expected value lexer tests
Merge pull request #16 from RossJHagan/lexer-tests

Adds basic expected value lexer tests