Implement `eye` function
Add tests
Implement `diag`
Add tests for `diag`
Implement `ones` function and `zeros` function
Add tests for `ones` and `zeros`
Refactor `eye` to use `diag`
Fix test failure: Avoid comapring `unsigned` and `int`
Refactor code as suggested by Thomas Hisch

Below is the original comment:
https://github.com/sympy/csympy/pull/332#discussion_r20773992
Merge pull request #332 from thilinarmtb/matrix_functions

Convenient functions for Matrices