Merge pull request #23 from mwiebe/travisci_py26

Clean up the .travis.yml a bit, add python 2.6
A simple lexer for the datashape grammar
Add first test of the datashape lexer
Add a lexer test for invalid tokens
Add tests for integer token and whitespace in lexer
Tighten up the string token in the lexer, add tests for it
Convert the lexer into a generator which returns a sequence of namedtuples
Add outline of datashape parser object
Start translating the production rules into functions