Doesn't ssupport ~........... escaping syntax

[yotam-eshel]

This kind of syntax is used extensively in lesshat (http://lesshat.com/), therefore lesshat doesn't compile on less4j

[SomMeri]

This is going to be possible using custom functions https://github.com/SomMeri/less4j/wiki/Extending-Less-Language which are already implemented, but do not support ~... and ... syntaxes.

Starting with next release:

• ~... will be treated as function named ~`
• ... will be treated as function named `

The advantage is that anyone will be able to implement them however he likes and use any language he finds useful.

I'm not sure whether or when I will create "official" javascript implementation, but anyone will be able to do so. In any case, it will be stored in separate repository. I do not want less4j to depend on Rhino or other javascript runtime, because only some projects will use it.

[SomMeri]

I will close this as duplicate of #22.