Update eslint, retext

Additionally removes retext as a peer-dependency
Add retext-content as a dev-dependency
Refactor spec

Includes changes for retext@0.2.0.
Includes retext-content.
Remove testling
Update copyright in Readme.md
Fix property order in package.json
Update Installation in docs

- Fix casing of NPM > npm;
- Remove component, which never worked.
Update .gitignore, .npmignore
Remove browser test
Remove `npm update` from travis
Add npm deployment to travis
Refactor API
Refactor Readme.md
Update changelog for 0.1.3
0.1.3