Major overhaul

* put different responsibilities into specific classes
  (not entirely done yet)
** Git class for invoking hooks
** Ledger class for calling ledger
* changes in the generated JSON output
Move budget, register, balance stuff into separate classes
Bump version number

The changes introduce major incompatibilities in the API so I bump the
version number to 2.0. Yeah. This project is awesome. Ledger is
awesome. And the inflation of awesome is awesome.
Remove date format from App
Add `transactions` service stubs
Add rspec and guard and implement a dumb parser
Add entry class and fix account parsing
Add entry class to respective http handler
Fix parsing for serialized transaction
Fix nullable values for transaction parser
Fix object type for json response
Create a ruby gem
Add rake as dependency
Move version.rb to the right directory
Fix version require path in gemspec file
Fix yml config when file does not exist
Add project org-file
Fix dependencies

The dependencies were not set inside the gemspec file.
Bump version number to 2.0.2
Add Gemfile.lock