Add all less.js functions

[SomMeri]

https://github.com/cloudhead/less.js/blob/master/lib/less/functions.js

[SomMeri]

Interesting special case for future pick function: less/less.js#1100 (comment)

[scottrippey]

Created Pull Request less/less.js#1110

[karlvr]

I need to have these functions so I've started working on this. I have so far implemented lighten, darken and hsla. More to come. Here's my work in progress branch, I shall submit a pull request once I've got a test case that will pass! (that may involve removing some things from the tests!)

https://github.com/karlvr/less4j/tree/color-functions

[SomMeri]

You did a lot of work, thank you. Just that we do no work on the same thing: I will assign what I'm working on to myself.
I'm currently working on media bubbling #42.

[SomMeri]

Documentation for functions: https://github.com/SomMeri/less4j/wiki/Less-Language-Built-In-Functions

Math functions are described, miscellaneous have only short descriptions and color numbers are not.