Add support for matrices creation in shell.
TODO:

• Write BNF rules for a matrix
• Add those rules to parser
• Add unit tests
• Add documentation in GUIDE.md

Example of syntax (based on MATLAB):

% Matrix with two rows. Each row has two elements. First row [1, 4], second [3, 2]
[1 4; 3 2]
% Matrix with two rows. Each row has three elements. First row [-1/2, 5/4, 5/2], second [1/2, 13/17, -9/2]
[-1/2 5/4 5/2; 1/2 13/17 -9/2]
% Matrix with one row. This row has three elements. It contains of [a, -3/2, x]
[a -3/2 x]

This syntax does not allow arithmetic expressions apart from scalars and variables, as e.g., expression

[3/4 -2/1]

can be interpreted either as [3/4, -2/1] or [-5/4].