Remove `isFunction` fallback from `modern` builds
Add `QUnit.config.noglobals` to build tests.
Make `optionsToArray` remove falsey values.
Clarify docs for `callback` use in `_.first`, `_.initial`, `_.last`, and `_.rest`. [ci skip] [closes #189]
Add doc not for chaining support in custom builds and tweak support rules in build.js. [closes #193]
Merge pull request #192 from phated/master

Implement `mkdir -p` for `--output` build option.
Move `mkdir -p` functionality to its own module and cleanup `--output` build tests.
Fix build.
Cleanup build tests and inline `_.mixin` when it's removed to preserve chaining behavior.
Add `path.sep` for older versions of Node.js.
Ensure all temp folders made during the `--output` build tests are removed.
Ensure relative paths work with `--output` and `template=…` build options.
Cleanup perf/perf.js and test/test.js.
Update vendors.
Simplify build/mkdirp-sync.js.
Cleanup comments in various source files.
Add `rhino -require` to the run-test.sh.
Fix `lodash.underscore` usage example in README.md. [ci skip] [closes #194]
Remove `isJSC` in `mobile` and `underscore` builds. [closes #196]
Make `_.runInContext` not require a fully populated `context` object.