Merge pull request #43 from cmaumet/master

Write out boolean type in PROV-N
Fix bundles in document graph output
Using StringIO instead of BytesIO
Fixed namespace scope inheritance in decoding bundles
Refactored the intefacing classes, added ProvJSONEncoder and ProvJSONDecoder
Fixed typo in the previous commit
Fixed resolving QualifiedName strings whose prefixes belong to a renamed Namespace
 Namespace pointing to the same URI of an existing namespace will not be added to NamespaceManager but will reuse the existing namespace
Added more QualifiedName constants for convenience
Fixed: UTF-8 encoding for prov.dot
Renamed Literal.get_value(), Literal.get_datatype(), and Literal.get_langtag() and made them properties
enh: add travis testing file
Added JSON test filed from ProvToolbox and unification tests
All the ProvToolbox's JSON was generated by the version https://github.com/trungdong/ProvToolbox/commit/bf13da78a5cdc409571fc9cbe9454597e4dd31fc with the dictionary-related files removed.
Unification test cases are taken from https://dvcs.w3.org/hg/prov/raw-file/default/testcases/process.html (only 9 at the moment)

Note: These are the files missing in #47
Merge remote-tracking branch 'upstream/master' into enh/travis

* upstream/master:
  Added JSON test filed from ProvToolbox and unification tests All the ProvToolbox's JSON was generated by the version https://github.com/trungdong/ProvToolbox/commit/bf13da78a5cdc409571fc9cbe9454597e4dd31fc with the dictionary-related files removed. Unification test cases are taken from https://dvcs.w3.org/hg/prov/raw-file/default/testcases/process.html (only 9 at the moment)
fix: updated dateutil name
fix: added python versions to tests
fix: support for 2.6 set
fix: more set fixes
fix: added support for asserts to unittest
fix: added assertLess
fix: remove checking for py3k
fix: remove redundant ls