feat(support): implement Markdown parser

[faustbrian]

Implement a markdown parser that supports CommonMark and FrontMatter through https://github.com/jxson/front-matter and https://github.com/jonschlinkert/remarkable.

[codecov]

Codecov Report

Merging #470 into master will increase coverage by 0.16%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #470      +/-   ##
==========================================
+ Coverage   72.10%   72.27%   +0.16%     
==========================================
  Files          52       53       +1     
  Lines        1029     1035       +6     
  Branches       73       73              
==========================================
+ Hits          742      748       +6     
  Misses        258      258              
  Partials       29       29              

Flag	Coverage Δ
#unit	72.27% <100.00%> (+0.16%)	⬆️

Impacted Files	Coverage Δ
packages/platform-sdk-support/src/markdown.ts	100.00% <100.00%> (ø)

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