Fixed docs for Bokeh maps and type of Matplotlib Glasbey maps

[jbednar]

• Preserved versioning code (previously mistakenly fixed in colorcet/__init__.py rather than in the master assets/CET_to_py.py)
• Clarified docs to show which maps are Bokeh lists of RGB colors (fixes #69)
• Use Matplotlib ListedColormap instead of LinearSegmentedColormap for categorical (Glasbey) maps (fixes #39)

[codecov-commenter]

Codecov Report

Merging #79 (4920da0) into master (94f1207) will decrease coverage by 0.05%. The diff coverage is 96.87%.

@@            Coverage Diff             @@
##           master      #79      +/-   ##
==========================================
- Coverage   95.87%   95.82%   -0.06%     
==========================================
  Files           7        7              
  Lines        1574     1579       +5     
==========================================
+ Hits         1509     1513       +4     
- Misses         65       66       +1     

Impacted Files	Coverage Δ
colorcet/__init__.py	99.28% <96.87%> (-0.07%)	:arrow_down:

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