Release 0.5.1

Release 0.5.1 (2014-10-11)

Release notes:
* Improvements
  * Support for Oracle Ehnanced Adapter 1.5 and ActiveRecord 4.1, 4.2
  * Oracle 12c support
  * Better diagnostics output when ruby-oci8 initialization fails
* Bug fixes
  * Support for ruby-oci8 2.1.2+ preventing segfaults
  * Multi-thread support (applies to oci8 connections)
* Internal (development) improvements
  * Tests database connection enhancements (eazy connect syntax, allow service name != db name)
  * Tests migrated to rspec 3
  * Tests coverage migrated from rcov to simplecov
  * README update with how to run tests