Rewrite specification

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

Closes GH-17.
Closes GH-18.

Reviewed-by: Christian Murphy <[email protected]>
Reviewed-by: Ika <[email protected]>

Author: wooorm