1.4.0 version
Remove deprecated string interpolation
Correct handling of units.

width: 1cm - 5mm
=> width: 0.5cm (instead of -4cm)

@ratio: 100px/50px
=> @ratio == 2 (instead of 2px)
loosened restriction on css units (who knows what W3C will think up next)
Add Sass like extend
Fix bug global leaks, `;` to `,`
Fix combinator is not extended
Fix merge errors/problems and change format to ++
- Change the default behavior of "@import" to only import once.
- Add @import-multiple if for some insane reason you want multiple imports.
- Continue to support @import-once for backwards compatibility.
- Fixes #212.
Change extend format to :extend(.class); - part 1 - support for stand-alone &:extend(.class);
Fix unit comparing after merge
Rudimentary support for extend in selectors
Add additional test for nested selectors. Rebuild dist.
Correct unit merge
regenerate browser files
Added the square root function.
add a data-uri function

as described in a comment on #775
throw an error if data-uri is used in the browser

and move require('fs') into the function, so other things
still work in the browser.
guess the mimetype, and properly encode non-base64 uris
move data-uri tests to url.less so they are not run in the browser. add browser tests. make function return url() in the browser