Add classes for discontinuous axis

[eltos]

Description

Adds classes to help creating discontinuous axes

• Implement classes
• Add example & test
• Implement support for multiple discontinuities

import matplotlib.pyplot as plt
import numpy as np
import xplt

fig, ax = plt.subplots(figsize=(4.5, 3))
x = np.linspace(0, 10, 10000)
ax.plot(x, np.sin(2*np.pi*x))
ax.minorticks_on()
ax.grid()

ax.set_xscale('discontinuous_linear', breaks=[(2, 4),(6,9)], space=0.5)
ax.set_yscale('discontinuous_linear', breaks=[(-0.25, 0.25),], space=0.1, hide=True)