Add support for non-standard structures inside elements

[danielfernandez]

Reference: thymeleaf/thymeleaf#261

It seems some client-side technologies like ember.js can include macros inside tags themselves (see http://emberjs.com/guides/templates/binding-element-attributes/ ) which would result in a parsing error.

At first sight, this does not seem like a blocking problem because most times these templates will be inside <script> tags, and other solutions could be possible (like ignoring <script> contents or using a CDATA block). But anyway, it would be nice if attoparser could detect such unknown structures and just ignore them as a sort of "unknown inner block", passed as-is to the event system.

For example, the following blocks could be ignored:

• {...}, for any number of consecutive {'s.
• [...], for any number of consecutive ['s.
• (...), for any number of consecutive ('s.
• <...>, for any number of consecutive <'s.

[ghost]

Please add this feature if its possible.