Markup for doc strings

[tiffany352]

Makes Rink parse out the links and date strings when using the token format machinery. This is a new syntax in the definitions file with <abc> for links and #abc# for dates.

Replaced ansi_term with nu-ansi-term because the former was unmaintained. The latter comes with the ability to set hyperlinks.

[codecov]

Codecov Report

Attention: Patch coverage is 96.06557% with 12 lines in your changes are missing coverage. Please review.

Project coverage is 80.15%. Comparing base (c0aadc4) to head (da9467a).
Report is 1 commits behind head on master.

❗ Current head da9467a differs from pull request most recent head 21acc56

Please upload reports for the commit 21acc56 to get more accurate results.

Files	Patch %	Lines
cli/src/fmt.rs	94.61%	9 Missing ⚠️
cli/src/style_ser.rs	98.78%	1 Missing ⚠️
core/src/loader/load.rs	85.71%	1 Missing ⚠️
core/src/output/reply.rs	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #177      +/-   ##
==========================================
+ Coverage   76.09%   80.15%   +4.06%     
==========================================
  Files          41       42       +1     
  Lines        7383     7676     +293     
==========================================
+ Hits         5618     6153     +535     
+ Misses       1765     1523     -242     

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