Only symbolize strings in #symbolize_keys_recursively
Reduce number of intermediate objects in #symbolize_keys_recursively
Merge pull request #312 from ddfreyne/bug-allow-attributes-with-non-string-keys

Allow attributes with non-String keys
Merge branch 'release-3.6.x' of github.com:nanoc/nanoc into release-3.6.x
Lazy-require coffee-script (fixes #314)
Merge branch 'release-3.6.x' into release-3.x