unix line endings
Fix LICENSE year
Allow the comment to be on the same line as code

See <https://github.com/thlorenz/convert-source-map/issues/5>.

This is both about following the spec, and supporting real tools.

This change meant lots of changes in how each method works. See the
changelog.
Rename `.get` and `.remove` to `.{get,remove}From`

It simply reads better.
Add `.existsIn()`
Remove references to `this` to make methods detachable
Take advantage of `npm run <script>`