v3.0.0

• Allow including many templates without reaching recursion limits. Merge of
  #787. Thanks Gleb Khudyakov.
• Allow explicitly setting null (aka none) as the value of a variable;
  don't ignore that value and look on up the frame stack or context. Fixes
  #478. Thanks Jonny Gerig
  Meyer for the report.
• Execute blocks in a child frame that can't write to its parent. This means
  that vars set inside blocks will not leak outside of the block, base
  templates can no longer see vars set in templates that inherit them, and
  super() can no longer set vars in its calling scope. Fixes the inheritance
  portion of #561, which
  fully closes that issue. Thanks legutierr for the report.
• Prevent macros from seeing or affecting their calling scope. Merge of
  #667.
• Fix handling of macro arg with default value which shares a name with another
  macro. Merge of #791.
• Add support for the spaces parameter in the dump template filter.
  Merge of #868.
  Thanks Jesse Eikema
• Add verbatim as an alias of raw for compatibility with Twig.
  Merge of #874.
• Add new nl2br filter. Thanks Marc-Aurèle Darche
• Add support for python's list.append with Jinja compat enabled. Thanks
  Conor Flannigan.
• Add variables whitespace control.