Fixed a bug where an error could be thrown due to an empty XML string.

Error: DOMDocument::loadXML(): Empty string supplied as input.

Occurred when creating a new transaction based on an account credit.
tests; added for PR #62
tests; clean up
release 2.2.2
Remove old taxable parameter.
Call Recurly_Resource's constructor

PHP doesn't call parent constructors automagically, so if you override
it you need to call `parent::__construct()` yourself.
Switch to PHPUnit for tests
Rename test/ to Tests/ so PHPUnit finds them.
Let Travis run our tests
Add Travis build status and cleanup README

Wrap long lines, use better syntax highlighting, etc
Test Plan's total_billing_cycles

Also puts the assertion arguments in the expected order.
Merge pull request #66 from recurly/phpunit-tests

Switch to PHPUnit for tests
Include null attributes in XML

This will allow plan.total_billing_cycles to be changed to continuous
auto renewal.

Also changes the XML we generate to avoid empty tags favoring `<foo></foo>`
over `<foo/>`. This matches the sample XML in our docs.
Merge pull request #68 from recurly/send-null-attributes

Include null attributes in XML
Release notes for 2.2.3
Each of the push notification types end with '_notification'. Updating comment to reflect that.
remove brackets in comment since this isn't a proper array anyway
Merge pull request #73 from richardkmiller/fix_push_notification_comment

Fix commenting in Recurly_PushNotification to match `type`
Update XML in fixtures
Add tests for parsing Adjusments