dotted names in sorting
Merge pull request #69 from Evgenus/master

dotted names in sorting
fixing "global name DuplicateKeyError is not defined" error
Merge pull request #70 from toddtomkinson/fix_DuplicateKeyError_import

fixing "global name DuplicateKeyError is not defined" error
Acknowledgements
Forbid non-string keys (#71)
Internalize dicts on updates