Add support for [[Wikilinks]]

[ryanwwest]

This adds support for wikilinks in the same way that URLs are supported. I.e., upon pasting if text is already selected, both the clipboard contents and the selected text are parsed to see if one contains a [[wikilink]]. If so, it takes the wikilink text and gives it text for display using the non-wikilink text. For example:

selected text is [[really-long-name-of-a-note]] and clipboard text is see here. After pasting, the result becomes [[really-long-name-of-a-note|see here]]. The result would be the same if 'selected text' and 'clipboard text' assumed opposite roles.

[ryanwwest]

This is meant to address #31.