Add multiline support for variables, fix @markup implementation & update docs

[darcyclarke]

Slowly getting this project up to snuff. Updated the parsing implementation so that it now supports multiline variables (#56). This also fixes multiple @markup variables (#54). Along with this change, I've gone ahead and refactored how we provide information/variables to the callback functions passed to dss.parser(). We give you interesting information like this.line.from and this.line.to which are line numbers associated with the contents of a variable (#53).

Documentation had not been touched in a long time, so I've now update it and will cut a new release once I'm happy that all of these changes aren't breaking anything they shouldn't be. The API has changed slightly (as noted above) so I'm a bit torn as to whether I should make this a major release or not (thoughts/opinions welcome).

I may write a custom parser to show how you can address #51, providing support for Jade, Markdown, HAML or whatever language for your @markup example.

[jeffjewiss]

Do you want feedback on this kind of stuff? A little hard to discuss if the PRs are just merged 🚢 right away. 💥

[darcyclarke]

@jeffjewiss going forward, yes. Just had to get this up-to-date and push through necessary work. I'm done playing god on master for this project 😉 That said, the other repos you saw pop up, they're fair game for the next few days. This repo (ie. the DSS parser) is the most important, so it makes sense that it is taken the most seriously.

[darcyclarke]

It should also be noted that I haven't cut a new release, and won't until things are settled a bit. That means that anyone still referencing the project via npm isn't affected by my hazardous merging.