hatch functions

[mathause]

• [x] Closes #62
• [ ] Tests added
• [ ] Passes isort . && black . && flake8
• [ ] Fully documented, including CHANGELOG.md

import cartopy.crs as ccrs
import matplotlib.pyplot as plt
import mplotutils as mpu
import xarray as xr

%matplotlib qt

air = xr.tutorial.open_dataset("air_temperature")

f, ax = plt.subplots()
air.air.isel(time=0).plot(ax=ax)

mpu.hatch(ax, air.air.isel(time=0) < 250, "///", "None")

plt.legend()

# ===========

f, ax = plt.subplots(subplot_kw={"projection": ccrs.PlateCarree()})
ax.coastlines()

air.air.isel(time=0).plot(ax=ax, transform=ccrs.PlateCarree())
mpu.hatch_regional_map(ax, air.air.isel(time=0) < 250, "///", "None", color="w")

plt.legend()