Robustness of GRMustacheErrorHandlingTest
Test that the boolean value of collection items is ignored when iterating collections
Remove pointless tests from GRMustacheRenderingObjectTest
Introduce optional [GRMustacheRendering mustacheBoolValue] method, which controls whether section tags are rendered or not. Deprecate GRMustacheTagTypeInvertedSection.
Remove pointless use of GRMustacheTagTypeInvertedSection in standard library helpers and NSFormatter
Introduce `zip` filter in the standard library. Tests for features introduced in v7.2
Rendering Object Guide: documentation of the mustacheBoolValue methid