Adds support to Ruby for encrypting, decrypting, signing and validating the signatures of XML documents, according to the [XML Encryption Syntax and Processing](http://www.w3.org/TR/xmlenc-core/) standard, and the [XML Signature Syntax and Processing](http://www.w3.org/TR/xmldsig-core/) standard by wrapping around the [xmlsec](http://www.aleksey.com/xmlsec) C library and adding relevant methods to `Nokogiri::XML::Document`. Implementation is based off nokogiri-xmlsec by Colin MacKenzie IV with very heavy modifications.