Re-write some of the Python scripts

I modified the scripts in the folder `$CUIBM_DIR/scripts/python/`

to make them a little bit more readable, using **Numpy** features.

I added some comments, docstrings. The parser has been pushed inside a function.
In some cases I added a flag `--show` to the parser, to display the geometry in a figure.

Scripts modified:
* `analyseVorticity.py`
* `elements.py`
* `ellipse.py`
* `naca00xx.py`
* `plotVelocity.py`
* `plotVorticity.py`
* `readData.py`
* `rotateBody.py`

Please, @anushkrish , have a look at those and tell me what you think. Thanks!

Also, I did not touch the script `regularise.py`, because I have something similar for `pyIBM`.
Please, have a look [here](https://github.com/mesnardo/pyIBM/blob/master/scripts/geometry_discretization.py).
This script allows re-discretization (number of elements or segment-length), rotation, translation, scaling.
Tell me if this could replace the scripts `regularise.py` and `rotateBody.py` in **cuIBM**.