getting started
re-organise, add some content and tidy up features
Merge branch 'master' of https://github.com/less/less-docs

Conflicts:
	content/features/mixins-recursive-loops.md
changes after latest merge
remove empty sections in variables
document mixins
fixed color-blending multiply example.
content/color-operations.md: updated with  https://github.com/less/less.js/pull/1669 changes (+ some minor reformatting)
content/color-operations.md: a few minor updates