Remove scripts from package.json

Duplicated in Makefile, and they're already gotten stale
Update gitignore
Add `values`
Add `extend`
Add `has`
Add `forIn`
Add `forInRight`
Shorten import
Amend `forIn-` method descriptions
Add `forOwn`
Add `forOwnRight`
Add `clone`
Update internal slice notes
Add placeholder re: browser support
Add docs for `clone`
Add `invert`
Add `mapObject`
Add `omit`
Make `omit` ignore non-string omissions
Return early from `omit` when possible