SMALL API CHANGE: is_valid->isvalid, plus some pretty print changes, etc

* BREAKING API change: is_valid() changed to isvalid
* Implements a __len__ method on FeatureVector
* Prettier prints out FeatureWeight report info
* New data attributes on class FeatureSet:
** name
** contiguous_imagenames_list (contiguous_imagenames_list:imagenames_list::data_matrix:data_list)
* Better checking for interpolation_coefficients are present on FeatureSet instances
* Added quiet argument BaseGragh creation
Merge colettace:issue_27 feature branch

New methods:
- NewShuffleSplit to perform cross-validation.
- PerSampleStatistics renamed from PredictedValueAnalysis
- New module pychrm.ArtificialFeatureSets
- Unit tests for just about all new functionality
Fix inacurate docstring for ArtificialFeatureSets functions
Merge pull request #33 from colettace/june2014_release

Fix inacurate docstring for ArtificialFeatureSets functions
Merge pull request #31 from wnd-charm/june2014_release

June2014 release