WIP first tests and implementation for variables detection
Use real async jasmine spec for searchColor tests
:bug: Fix false positive match in `canHandle`
:fire: Remove unnecessary callback in `searchColor`
Implement first parsing of less variables in buffers
Implement variable search for sass, scss and stylus syntax
Add a `color` property in buffer scan results

The `color` property stores a `Color` object corresponding
to the found color.
Implement variables parsing before searching for colors
Prepare 1.5.0 release