Merge pull request #86 from jgrewe/tutorial

an extended set of tutorials...

Awesome!!
Merge pull request #90 from jgrewe/tutorial

Tutorial: using Features I

lgtm
Remove mixins from namespace after monkey patching

After their job is done, they can go home ;-)
DataSet → DataSetProxy
Export nix::DataSet + make it base for DataArray

Need a wrapper clase since DataSet is abstract.
NB: This needs nix pr #414 merged due to DataSet::dataType()
DataSetProxy→DataSetMixin, DataArray is a DataSet
move ::data_extent prop from DataArray to DataSet
[test] Adap for DataArray is a DataSet change
Merge pull request #92 from gicmo/dataset

Export nix::DataSet and make it a base of DataArray
DataView: Export as nix.core.DataView
MulitTag: export retrieveData (as retrieve_data)
[test] MultiTag.retrieve_data tests
Move "data_type" prop from DataArray to DataSet
Move DataSet export logic into its own file

It was getting quite crowded in PyDataArray.cpp. Now there is
space in PyDataSet.cpp.
PyDataSet.arrayEnsureShapeAndCount: by-ref params

Actually wasn't doing anything before. Doh!
Merge pull request #91 from gicmo/mixin_namespace

Remove mixins from namespace after monkey patching
Merge pull request #93 from gicmo/retrieveData

Support for MultiTag.retrieve_data
[tutorial] add example code and figure for taggedFeatures
[tutorial] add taggedFeature example to tutorials.rst
[tutorial] rename of tagged example figure to match pattern