Get currency through order, not global config

Change-Id: Ic06a24d7d8a7c199316aba76880a2f6f518e3685

Fixes #5
Add mention of teclacolorida blog post
Fixes Thor happiness.

Thor has already been required. This may cause Bundler to malfunction
in unexpected ways.
Append routes.
Remove Versionfile.

No longer used.
Base engine adjustments.

- Add same version style that capybara gem uses.
- Cleanup unnecessary comments.
- White space removal.
- Gemspec improvments.
- Add a tiny passing spec.
Add Travis config.
Auth device has to use 2-0-stable branch.
Changed license to md and updated readme.

- License looks much better in markdown format.
- Add standard contributing info.
Maybe not spam IRC channel ;)
Specify branches for spree + spree_auth_devise
Begin writing a real test for PayPal

This walks through all the way up to confirm, which is still to be implemented
Switch to using PayPal's Merchant SDK

ActiveMerchant's PayPal Express's code is very old (using version 72, rather than 90-something), and doesn't allow you to pass shipping + tax rates like this one does
Mention PayPal's Merchant Ruby SDK in README
Add instructions for installing the extension
Allow mode to be set to 'live'
Add instructions to README for Spree setup
Allow preferred_server to be set to 'live'

... For those daring enough.
Add 'Production' setup instructions to README
Include link to PayPal's documentation on API credentials