Implement letter and digit parsers
Remove corresponding declarations from parsy_test.py
Import new parsers for test
Switch to unittest for testing
Still not using .assert...() methods
Use .assert...() methods instead of plain asserts
Convert sexpr_test.py to use unittest
Rename files to make unittest Test Discovery work
Merge pull request #2 from bugaevc/unittest

Testing with unittest
make setup.py executable
rm an unused function
add fail and use lambdas
fix whitespace
fix whitespace
improve ParseError
add descriptions for custom error messages
add mark and index to get index info
rm unused Result
add line_info, make mark yield line info
retroactively bump the version :x