Rewrite specification

* Reword `text` > `literal` (GH-17)
* Add introduction
* Reword definitions, terms
* Add more terms
* Add references
* Add more acknowledgements

Closes GH-17.

Reviewed-by: Christian Murphy <Christian.Murphy.42@gmail.com>
Reviewed-by: Ika <ikatyang@gmail.com>

Author: wooorm