Add pretty matrix output

[brinza888]

Include for this library Sympy or just standard fractions.
Also need to support roots.

[brinza888]

Stage 1

Implement Matrix method .pretty(), that will be return string with formatted matrix.
Main idea on this stage is to make support of fractions. If matrix element can not be represented as decimal, .pretty() should represent this element as fraction (even improper).

Example:
Here is element [0][1] is fixed point decimal got by dividing 2 by 3 (2/3). Same with 1 divided by 3 (element [1][0])

10.5 0.666
0.333 0.256

To avoid fixed point values for periodic fractions we will use just fraction representation.

10.5 1/6
1/3 0.256