v1.0.20

Added make_histograms functionality from popmon to dataframes

- Add n_dim and datatype properties to all histogram types
- Added unit test of new datetype property of histograms
- Moved sparksql.py to new dfinterface directory
- Added addmethods functions for spark and pandas
- Set default identity function for quantity for each histogram type
- Added make_histograms functionality from popmon to spark and pandas dataframes
- force sparselybin origin and binwidth to be float always
- Fix spark filling of multiple histograms
- make_histograms now includes all available histograms
- Updated docs strings for histogram makers
- Accept list and tuple as numpy array
- 1d plotting for irregularlybin and centrallybin histrograms
- Added default values for time_width and time_offset
- working unit tests for pandas_histogrammar and spark_histogrammar
- handy monkey patch functions for pandas and spark dataframes
- plot function for 2d irregularlybin
- in categorize plot sort labels alphabetically
- implemented matplotlib function for most 2d count histograms
- autopep8 of primitives
- fix flake8 errors of all code
- Bump version to 1.0.20
- added json dumper util function
- added bin_centers function for categorize histograms
- popmon reference in histogram_filler_base.py transform function
- fix small assignment bug in Sum histogram
- make convenience definitions work
- add basic tutorial notebook for histogrammar
- added advanced histogrammar notebook
- unit tests for notebooks
- added manifest and notice file
- update of readme.rst file
- remove python 2.7 and 3.4, 3.5 from travis config