breakpoint-slicer syntax support added. tests to follow
Added tests
small edits

- remove scale-length (breaks if scale overridden)
- change desktop cutoff to 1050px
- use desktop and mobile cutoff variables in base scale
- adjust tests accordingly
move usage below API docs in readme
update docs
Merge pull request #3 from jenius/slicer

breakpoint-slicer syntax support added.