4.0.7

@kratsg implemented memberwise serialization for std::pair: PR #298, #301.

@nsmith- made sources and caches pickleable: PR #302.

@wiso fixed a typo in the documentation: PR #315.

@henryiii cleaned up the build procedure and got Python 2.7 added to the regular tests: PR #316, #317, #319.

@jpivarski fixed a bug that exposed internal JaggedArray objects (if they're empty): PR #304. Added histograms to the regular tests: PR #305. Fixed "file://" handling on Windows: PR #328.

@jpivarski also started developing file-writing (though it's not ready yet): PR #320, #322, #329, and fea04ad.