Tests, code coverage and some new functionality

[alanocallaghan]

This implements native plotly heatmaps (#20), font size params (#39), cellnote (#42), support for long data and altered mouseover labels (#37 and #36).

I will double check these edits before merging, this is merely an easy way to compare.

Basic tests and code coverage reporting are implemented here. I'm not 100% about how to add a coverage badge, though you could make an account on codecov.io to add it yourself

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@db6f9d0). Click here to learn what that means.
The diff coverage is 88%.

@@            Coverage Diff            @@
##             master      #43   +/-   ##
=========================================
  Coverage          ?   87.78%           
=========================================
  Files             ?        6           
  Lines             ?      794           
  Branches          ?        0           
=========================================
  Hits              ?      697           
  Misses            ?       97           
  Partials          ?        0

Impacted Files	Coverage Δ
R/percentize.R	25.64% <100%> (ø)
R/heatmapr.R	87.87% <81.25%> (ø)
R/plots.R	85.49% <85.49%> (ø)
R/heatmaply.R	96.16% <93.54%> (ø)

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[talgalili]

I added a badge. Great set of tests - thanks!

[alanocallaghan]

Hopefully if we split out some of the functionality the tests can become a bit more granular, but it's a good start. I'm glad to have put them in, because they keep catching mistakes :)