Update using-less.md

Basically added the Environment description. Since there is no stated options for the environment, I went ahead and listed them and pasted the examples to be used.
Add est into projects using LESS
Merge pull request #153 from Justineo/patch-1

Add est into projects using LESS
Removed ambiguity in wording on variables and namespaces.

See http://stackoverflow.com/questions/8658270/less-css-syntax-error-when-referencing-variable-from-namespace
Merge pull request #154 from rnorbauer/patch-1

Removed ambiguity in wording on variables and namespaces.
Merge pull request #152 from sparatan117/patch-1

Update using-less.md
Typo "who will sees". Should be "who will see"
Merge pull request #155 from adrianvoica/patch-1

Typo "who will sees". Should be "who will see"
Updated using-less.md with some links.
added nodeMirror to editors list

let me know if this is appropriate
Merge pull request #157 from soliton4/patch-1

added nodeMirror to editors list
editors-and-plugins.md: polished nodeMirror description.
Update frameworks-using-less.md

Added my mixin library to the list
Merge pull request #158 from pixelass/patch-1

Update frameworks-using-less.md
Updated using-less.md with some links.
Documented `+_` property merge operator.
Merge pull request #159 from seven-phases-max/space-property-merge

Space property merge
Merge pull request #156 from seven-phases-max/master

Updated using-less.md with some links.
Add info for PhantomJS