Add pkgdown site.

[michaelquinn32]

Closes #426

[codecov-io]

Codecov Report

Merging #431 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #431   +/-   ##
========================================
  Coverage    96.85%   96.85%           
========================================
  Files           13       13           
  Lines          382      382           
========================================
  Hits           370      370           
  Misses          12       12

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c287eb7...7574985. Read the comment docs.