Add autocomplete helper

[jdfreder]

Try implementing something similar to Sublime's autocomplete, which looks at all of the words used in the document.

[jdfreder]

@Kevsani here's a medium/low hanging fruit if you're still interested in contributing. You may want me to do #53 first though, so you have API docs to look at.

[jdfreder]

Removing this feature from the 1.0 milestone.