Inline link style option

Added an option to generate Markdown links in the *inline* style instead of the *reference* style. This option is supported in both the API (via `inline` option) and CLI (via `-i` and `--inline` switches).

### Inline

    [my link](/path/to/page "my title")

### Reference (existing)

    [my link][0]

    [0]: /path/to/page "my title"

Read John Grubers original [documentation on links](http://daringfireball.net/projects/markdown/syntax#link) for more information.