Implementing HTML Validators

@fosdev DO NOT MERGE. Please have a look at initial commit. Decided to change from validators to attributes in YML, since not all attributes are actually validation attributes. It will help to support attributes like 'placeholder'. The issue here is that attributes must be given as Hash: 
  - required: required     <- which is actually a valid HTML5 notation.

This is due to XmlMarkup: when you try specify <input type="text" name="text" required/> it will consider XML not well formed and raise an error. I still need add, fix and update specs.