WIP: Start attempt to use altair for plotting

[mattpitkin]

Start trying out using Altair to make plots if requested. Refs #3. Supercedes #31 as I've changed the branch name to be more appropriate.

[pep8speaks]

Hello @mattpitkin! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file psrqpy/search.py:

Line 2687:101: E501 line too long (133 > 100 characters)
Line 2713:1: W293 blank line contains whitespace
Line 2834:101: E501 line too long (113 > 100 characters)
Line 2837:101: E501 line too long (108 > 100 characters)
Line 2839:101: E501 line too long (108 > 100 characters)
Line 2840:101: E501 line too long (160 > 100 characters)
Line 2842:101: E501 line too long (110 > 100 characters)
Line 2843:101: E501 line too long (110 > 100 characters)
Line 2846:1: W293 blank line contains whitespace
Line 2939:25: W291 trailing whitespace

Comment last updated at 2020-01-13 23:21:08 UTC

[mattpitkin]

Another thing to add in this the ability to use a set a 'symlog' scale. This is currently not implemented in Atlair (vega/altair#1077) due to not being implemented in a chain of dependencies going back through Vega-Lite, Vega and d3. When/if these are resolved I can add this option.

[codecov]

Codecov Report

Merging #33 into master will decrease coverage by 0.82%.
The diff coverage is 31.74%.

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
- Coverage   70.54%   69.71%   -0.83%     
==========================================
  Files           4        4              
  Lines        2241     2282      +41     
  Branches      424      442      +18     
==========================================
+ Hits         1581     1591      +10     
- Misses        478      500      +22     
- Partials      182      191       +9

Impacted Files	Coverage Δ
psrqpy/search.py	71.97% <31.74%> (-1.22%)	⬇️
psrqpy/utils.py	57.65% <0%> (-0.4%)	⬇️

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[mattpitkin]

symlog is now supported by altair, so I can add this option.

[mattpitkin]

To output html that contains the chart, and can also still be used interactively, see here.

[mattpitkin]

Also, maybe look at using rich displays options for "automatic" generation using altair if using a Jupyter notebook.