Pymatrices

**Removed a bug in `pm.determinantOf()` function**.

Added the function, `pm.isInvolutory()`.
Updated PyPI Description Notes. _Refer [Here](https://pypi.org/project/pymatrices/0.0.4/)_

1. Added the following functions :-
- `pm.isIdempotent()`
- `pm.isNilpotent()`
- `pm.isNull()`
- `pm.O()`
2. Improvised Description Notes.

**Stable Release**
***For Information, Refer 'readme'***