Add HTML report output for cli

[rbuckton]

Add support for a html report output in the grammarkdown cli:

grammarkdown source.grammar --format html

This would have the following characteristics:

• Grammar emit to a <dl> (HTML definition list).
  • LHS of each production emit as a <dt> (HTML definition term).
    • id attribute for hyperlink navigation using url fragments (e.g. #Identifier).
    • Identifier as a <var> (HTML variable).
    • Identifier linked via <a> (HTML anchor/link) to an index at the end of the report.
  • Production Parameters linked via <a> (HTML anchor/link) to an index at the end of the report.
  • RHS of each production emit as a <dd> (HTML definition)
    • id attribute for hyperlink navigation using url fragments (e.g. #Identifier-AlternateId).
  • Each Nonterminal is enclosed in a <var> (HTML variable) element.
  • Each Nonterminal is linked via <a> (HTML anchor/link) to the first instance of the declaring production.
  • Nonterminal arguments linked via <a> to the first instance of the declaring parameter.
  • Each Terminal is enclosed in a <kbd> (HTML keyboard input) element.
• Index following the grammar:
  • Entries for each Nonterminal used in the grammar.
  • Unordered list of each production in which the Nonterminal is used.

Example:

<section id="grammar">
<h1>Grammar</h1>
<dl class="grammar">
  ...
  <dt id="ImportDeclaration">
    <var><a href="#index-ImportDeclaration">ImportDeclaration</a></var>
  </dt>
  <dd id="ImportDeclaration-ade9f438">
    <span>
      <kbd>import</kbd>
      <var><a href="#ImportClause">ImportClause</a></var>
      <var><a href="#FromClause">FromClause</a></var>
      <kbd>;</kbd>
    </span>
  </dd>
  <dd>
    <span>
      <kbd>import</kbd>
      <var><a href="#ModuleSpecifier">ModuleSpecifier</a></var>
      <kbd>;</kbd>
    </span>
  </dd>

  <dt id="ImportClause">
    <var><a href="#index-ImportClause">ImportClause</a></var>
  </dt>
  ...
</dl>
</section>

<section id="index">
<h1>Index</h1>
<dl class="index">
  <dt id="index-ImportClause">
    <var><a href="#ImportClause">ImportClause</a></var>
  </dt>
  <dd>
    <var><a href="#ImportDeclaration">ImportDeclaration</a></var> : 
    <span>
      <kbd>import</kbd>
      <var>ImportClause</var>
      <var><a href="#FromClause">FromClause</a></var>
      <kbd>;</kbd>
    </span>
  </dd>
  ...
</dl>
</section>