PR for v.1.3.0

[hcpchris]

• Closes Serialize DataCore descendents to array of primitives rather than object when possible #77
• Closes Can't display x axis as category strings in bar chart #67
• Closes Add ability to retrieve required <script> tags as both a list and a string. #78
• Closes BUG: Creating series from DataFrame does not serialize Timestamp object to MILLISECONDS from Unix epoch #74

[codecov]

Codecov Report

Merging #81 (454335a) into master (88a802b) will increase coverage by 0.19%.
Report is 14 commits behind head on master.
The diff coverage is 82.08%.

@@            Coverage Diff             @@
##           master      #81      +/-   ##
==========================================
+ Coverage   90.31%   90.50%   +0.19%     
==========================================
  Files         206      206              
  Lines       27495    27815     +320     
  Branches     1786     1889     +103     
==========================================
+ Hits        24831    25175     +344     
+ Misses       1974     1926      -48     
- Partials      690      714      +24     

Files Changed	Coverage Δ
highcharts_core/options/series/data/boxplot.py	81.76% <68.75%> (+1.90%)	⬆️
highcharts_core/options/series/data/bar.py	83.39% <76.92%> (+2.25%)	⬆️
highcharts_core/options/series/data/vector.py	79.26% <76.92%> (+9.09%)	⬆️
highcharts_core/options/series/data/cartesian.py	79.85% <78.12%> (+7.58%)	⬆️
...ighcharts_core/options/series/data/single_point.py	72.40% <81.81%> (+7.18%)	⬆️
highcharts_core/options/series/data/bullet.py	78.40% <82.60%> (+11.74%)	⬆️
highcharts_core/options/series/data/range.py	88.10% <82.60%> (+7.12%)	⬆️
highcharts_core/options/series/data/base.py	89.02% <83.33%> (-0.78%)	⬇️
highcharts_core/utility_functions.py	40.09% <85.71%> (+3.14%)	⬆️
highcharts_core/metaclasses.py	66.75% <86.48%> (+3.40%)	⬆️
... and 8 more

... and 1 file with indirect coverage changes