Move HelloRequest to subfolder.
Add EPP schemas for testing requests.
Add Mocha for testing.
Remove default test file
Add mocha and schema loading to test/helper
Add initial failing HelloRequest test
Add EPP::Request#xml_node method to fix validation.

Also add EPP::Request.enable_validation! method which disables the XML
Schema Instance xsi:schemaLocation attribute from being set as this
breaks the schema validation.
Call EPP::Request.enable_validation! in test/helper
Add EPP::LogoutRequest
Use EPP::LogoutRequest in EPP::Server
Add LogoutRequest to EPP module autoloading
Add EPP::LoginRequest class
Use EPP::LoginRequest in EPP::Server
Add tests for EPP::Request
Add some tests for EPP::Server
Add tests for EPP::Client