make tests work again

- remove crazy comments
- remove main test (doesn't do anything)
- make parse test pass
move test data to test folder
code cleanup - remove random comments
remove underscore dep
pin xml2json dep
add serialize method

serialize takes a header and body objects and returns a valid OFX body.
remove transaction processing

this library is only about parsing or serializing OFX files and not
about processing the result. That is left to higher up users.
update the README

- cleanup some comments
- add documentation for serialize method