Extend the syntax

[michaelelfial]

It seems that the proposed syntax extension for variables support meets only positive and neutral reactions. So, it will be implemented, but one question arises. The concept of variables is not part of the current implementation of the language and is achieved through external library. Integrating the feature in the language will make such a library or built-in support required or it will be possible to have implementation that crashes if the syntax is used, but the library is missing. Any opinions?

[michaelelfial]

Done but merge in master and develop is pending along with at least minimal improvements in the documentation.