More support for metatags

Changelog

General Fixes typo
Minor bugs and improved code

• Metags (thanks @Biptaste )
  • setCanonical
  • getCanonical
  • setPrev
  • getPrev
  • setNext
  • getNext
  • addAlternateLanguage
  • addAlternateLanguages
  • getAlternateLanguages

Default canonical value (thanks for @mauri870 )
Buugfix #58 (thanks for @edbizarro )