Expose markdown-it enable/disable methods in loader options.

[dvogel]

This allows the component options to specify markdown-it rules to enable or disable. I needed this to take advantage of the default table support. I spent a while looking at markdown-it plugins that support different table syntaxes. It looks like they all override the basic table support, so using them from the component loader would depend on the rule being enabled.

[codecov-io]

Codecov Report

Merging #179 into develop will not change coverage. The diff coverage is n/a.

@@          Coverage Diff           @@
##           develop   #179   +/-   ##
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  Coverage      100%   100%           
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  Files            9      9           
  Lines          122    122           
  Branches        25     25           
======================================
  Hits           122    122

Impacted Files	Coverage Δ
src/convert.js	100% <ø> (ø)	:arrow_up:

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[gileswells]

@ticky would it be possible to consider this for inclusion? Currently there is no way to pass through rules to the enable and disable methods on MarkdownIt and this exposes that. So far as I can tell there isn't really a workaround to this limitation.