Optimize `_.escape`, `_.escapeRegExp`, and `_.unescape`.
Add comments to `_.escape` and `_.repeat`. [ci skip]
Use `TRAVIS_SECURE_ENV_VARS` instead of `TRAVIS_PULL_REQUEST`.
Ensure `_.escape`, `_.escapeRegExp`, & `_.unescape` can replacing multiple characters.
Ignore `isSorted` if `_.indexOf` is customized.
Simplify coveralls command in travis.yml.
Separate _.uniq isSorted logic to a helper
Cleanup previous commit.