Error handling improvements, compiler improvements, bug-fixes

• Cleaned up tests
• XML encoding will now be echoe'd by default in HHVM. An option
  echoXmlDoctype has been added to enable it manually
• Compiler now handles doctypes correctly (Fixed #2)
• Multiple extensions allowed via compiler's "extensions" options
  ("extension" has been removed) (Fixed #3)
• .jd can now be used as an extension by default (.jade still works)
• Some improved error handling
• Doctype tests
• Reworked the text-block lexing (#42)
• Changed attribute parsing so that expressions like function calls are
  possible (Fixed #41)
• Compiler will now always return Compiler-Exeptions, but will include
  the compiled file path (if any) in the message (Fixed #43)