re-factor plotting

[mathematicalmichael]

• Improve coverage
• Remove keyword arguments with default None that can be caught by **kwargs
  • Ensure documentation reflects this change. Maybe mention that it is a wrapper around pyplot?
• Adopt **kwargs structure (see below for example)

import matplotlib.pyplot as plt
import numpy as np
def wrap_fun(n=100,**kwargs):
    f = plt.figure()
    ax = f.add_subplot(111)
    ax.plot(np.random.rand(n), np.random.randn(n), **kwargs)
    plt.legend()
    plt.show()
    
wrap_fun(label='test', lw=3)