Corrected two failing tests with useless param

Ynab::BudgetParser#open required a file_path arg that wasn't being used
for anything. I removed the param and refactored the tests to match.
Cleaned up ruby loadpath

Moved errors.rb and budget_parser.rb further down /lib so that they
wouldn't pollute the require namespace.
Merge pull request #1 from JBangel/master

Correct BudgetParser#open which doesn't use it's parameter