New upstream release 1.7.0
    
    - https://github.com/less/less.js/blob/v1.7.0/CHANGELOG.md
    - Add support for rulesets in variables and passed to mixins to allow wrapping
    - Change luma to follow the w3c spec, luma is available as luminance. Contrast
      still uses luma so you may see differences if your threshold % is close to
      the existing calculated luma.
    - Upgraded clean css which means the --selectors-merge-mode is now renamed
      --compatibility
    - Add support for using variables with @keyframes, @namespace, @charset
    - Support property merging with +_ when spaces are needed and keep + for comma
      separated
    - Imports now always import once consistently- a race condition meant
      previously certain configurations would lead to a different ordering of
      files
    - Fix support for `.mixin(@args...)` when called with no args (e.g.
      `.mixin();`)
    - Do unit conversions with min and max functions. Don't pass through if not
      understood, throw an error
    - Allow % to be passed on its own to the unit function e.g. `unit(10, %)`
    - Fix a bug when comparing a unit value to a non-unit value if the unit-value
      was the multiple of another unit (e.g. cm, mm, deg etc.)
    - Fix mixins with media queries in import reference files not being put into
      the output (they now output, they used to incorrectly not)
    - Fix lint mode- now reports all errors
    - Fixed a small scope issue with & {} selector rulesets incorrectly making
      mixins visible- regression from 1.6.2
    - Browser- added log level "debug" at 3 to get less logging, The default has
      changed so unless you set the value to the default you won't see a
      difference
    - Browser- logLevel takes effect regardless of the environment (production/dev)
    - Browser- added postProcessor option, a function called to post-process the
      css before adding to the page
    - Browser- use the right request for file access in IE