Update README.md
Describe automatic logging of parsing and rendering errors
Nil input (template string, resource name, file path, URL) all have GRMutache return errors (fixes #56)
v6.7.5
Rendering nil NSString returns a GRMustacheErrorCodeTemplateNotFound error instead of a GRMustacheErrorCodeParseError.
FAQ: Is it possible to provide literal values in tags, or as filter arguments?
Revert "FAQ: Is it possible to provide literal values in tags, or as filter arguments?"

This reverts commit dad544d6371aa2003f35f85343290dbcf85854e9.
More TODO
Remove useless forward declaration
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importXXX methods WIP
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Prepare v6.8
v6.8.0
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Fix documentation
More visible links to Guides from the Reference
Add missing tests for mustacheTag:didRenderObject:as: and mustacheTag:didFailRenderingObject:withError:
Allow HTML.escape, javascript.escape, and URL.escape to escape the rendering of custom rendering objects.