Proposal for shell session highlighting

shell.html

<pre><samp class="hljs">$ <kbd class="hljs-shell"><span class="hljs-keyword">echo</span> <span class="hljs-string">'hello'</span></kbd>
hello
</samp></pre>

<pre><samp class="hljs">$ <kbd class="hljs-shell"><span class="hljs-keyword">git</span> <span class="hljs-option">-c</span> log <span class="hljs-option">-n2</span></kbd>
<span class="ansi-fg-yellow">commit f12c3c0434f144ee09c0dcfda2a819600baad2a4</span>
Author: Doug Bell <[email protected]>
Date:   Fri Jan 8 21:19:39 2016 -0600

    add better error message when include not found

    Now the error also includes the directories that were searched when the
    include wasn't found.

    Refs #428

<span class="ansi-fg-yellow">commit f9286e730accafc5fa3da0fe74ac589ddf9ba27b</span>
Author: Doug Bell <[email protected]>
Date:   Fri Jan 8 20:56:32 2016 -0600

    add parent dir to includes when rendering document

    Now, documents can include other files in their directory directly.
    Previously, only files in the theme directory could be included by
    default.

    Fixes #428
</pre>

<pre><samp class="hljs">$ <kbd class="hljs-shell"><span class="hljs-keyword">git</span> diff</kbd>
<b>diff --git a/README.mkdn b/README.mkdn</b>
<b>index 4fb06d6..4b83e15 100644</b>
<b>--- a/README.mkdn</b>
<b>+++ b/README.mkdn</b>
<span class="ansi-fg-cyan">@@ -80,3 +80,4 @@</span> This software is copyright (c) 2016 by Doug Bell.
 
 This is free software; you can redistribute it and/or modify it under
 the same terms as the Perl 5 programming language system itself.
<span class="ansi-fg-green">+</span><span class="ansi-fg-green">HELLO</span>
</samp></pre>

shell.markdown.txt

%# Run a simple shell command and display the output
%= system "echo 'hello'"

%# Run "git log -n2" and colorize the output, using "$" for the prompt (the default)
%= system --prompt => "$", "git log -n2"

%# Highlight an entire shell run, with prompt lines starting with $ or # (the default)
%= shell --prompt => "$|#", begin
$ git diff
diff --git a/README.mkdn b/README.mkdn
index 4fb06d6..4b83e15 100644
--- a/README.mkdn
+++ b/README.mkdn
@@ -80,3 +80,4 @@ This software is copyright (c) 2016 by Doug Bell.
 
 This is free software; you can redistribute it and/or modify it under
 the same terms as the Perl 5 programming language system itself.
+HELLO
% end