The CLI was completely rewrote. Changed dependency from yargs to commanderjs,
which is cleaner, faster and has no dependencies.
Also added a complete testsuite for the cli.
Closes#893, #894
Showdown now supports a simple HTML to Markdown converter.
**Usage:**
```
var conv = new showdown.Converter();
var md = conv.makeMarkdown('<a href="/url">a link</a>');
```
Closes#388, #233
