v0.3.0: Purity refactor

Purity refactor:

> all math-operators return real array, all math-operators are **pure**
functions.

Why:

+ completely avoid memory leaks;
+ boost performance;
+ parallel-ready.

This change addresses the need by:

+ eliminate all polymorphic, non pure function results.

Side effects:

It could be not fully backward compatible, however it seems quite so.