Nunjucks v2.2.2

Fixes:

• the body of {% raw %} and {% verbatim %} blocks is no longer highlighted
  as template code
• highlight {{ }}, {% %} and {# #} inside HTML attribute values,
  <script> and <style> blocks
• template tags are no longer parsed inside comments and strings, so
  {{ '{{' }} and {# {{ x }} #} work as expected
• support escape sequences in strings, e.g. {{ "say \"hi\"" }}
• keywords are no longer highlighted after a dot, e.g. {{ item.set }}
• handle whitespace control after a block filter: {% filter upper -%}
• add the missing endverbatim keyword
• highlight {{ }} and {% %} inside JSON scripts and style attributes

Features:

• add elseif keyword and is operator

Refactor:

• added a new nunjucks-raw context that embeds plain HTML until the matching
  {% endraw %} / {% endverbatim %}
• embedded JavaScript and CSS through the njk-js and njk-css contexts, which
  inject the nunjucks rules into them
• added nunjucks to the shared tag-attribute-value-content context
• removed pop: true from the nunjucks-statement, nunjucks-expression and
  nunjucks-comment blocks, so they no longer pop the surrounding context
• disabled the prototype inside the nunjucks-comment and nunjucks-strings
  contexts