Fix @-ignoring expressions

[cossssmin]

Description

This PR fixes a couple of issues with the regex used for expressions ignoring through the @{{ }} syntax.

Fixes #156

Fixes

• fixed an issue where ignored expressions were still being parsed if they were part of a text node; for example, given foo: 'bar' in locals, this:

   ignored: @{{ foo }}
   ignoredUnescaped: @{{{ foo }}}
   rendered: {{ foo }}
  

  ... was incorrectly being rendered as:

   ignored: @bar
   ignoredUnescaped: @{bar}
   rendered: {{ foo }}
  

  It is now correctly rendering as:

   ignored: {{ foo }}
   ignoredUnescaped: {{{ foo }}}
   rendered: bar
  

• fixed an issue with @-ignoring unescaped expressions ({{{ }}}); for example this:

   <p>ignoredUnescaped: @{{{ foo }}}</p>
  

  ... was rendered as:

   <p>ignoredUnescaped: @{bar}</p>
  

  It is now correctly rendered as:

   <p>ignoredUnescaped: {{{ foo }}}</p>
  

[cossssmin]

@Scrum please have a look, thanks!