Update dependencies

- Update retext, retext-visit, retext-content,
  retext-porter-stemmer.
Refactor spec
Remove testling
Update copyright in Readme.md
Fix property order in component.json, package.json, bower.json
Update .gitignore, .npmignore
Remove browser test
Refactor API
Remove example
Refactor Readme.md
Remove incorrect history
Update changelog for 0.1.0
0.1.0