Pass rc.cmap and rc.cycle arguments through respective constructor functions

[zxdawn]

Description

Since cycle supports cmaps, the input of cmap name in the configuration should be supported.

Steps to reproduce

import proplot as plot
import numpy as np

fig, axs = plot.subplots()
state = np.random.RandomState(51423)
data = (20 * state.rand(10, 21) - 10).cumsum(axis=0)

plot.rc.update({'cycle': 'plum', 'lines.linewidth': '5'})
lines = axs.plot(data[:, :5])

Expected behavior:
Like:

plot.rc.update({'lines.linewidth': '5'})
lines = axs.plot(data[:, :5], cycle='plum')

Actual behavior: [What actually happened]

Traceback (most recent call last):
  File "/home/xin/Desktop/test.py", line 11, in <module>
    plot.rc.update({'cycle': 'plum', 'lines.linewidth': '5'})
  File "/home/xin/Documents/Github/proplot/proplot/config.py", line 906, in update
    self.__setitem__(prefix + key, value)
  File "/home/xin/Documents/Github/proplot/proplot/config.py", line 410, in __setitem__
    kw_quick, kw_added, kw_params = self._get_param_dicts(key, value)
  File "/home/xin/Documents/Github/proplot/proplot/config.py", line 490, in _get_param_dicts
    colors = _get_cycle_colors(value)
  File "/home/xin/Documents/Github/proplot/proplot/config.py", line 1020, in _get_cycle_colors
    + ', '.join(map(repr, cycles)) + '.'
ValueError: Invalid cycle name 'plum'. Options are: '538', 'accent', 'classic', 'colorblind', 'colorblind10', 'dark2', 'default', 'flatui', 'ggplot', 'paired', 'pastel1', 'pastel2', 'qual1', 'qual2', 'set1', 'set2', 'set3', 'tab10', 'tab20', 'tab20b', 'tab20c'.

Proplot version

master branch

[lukelbd]

I'm going to close this as a duplicate of #69. When I add rc-param assignment validation it will be trivial to pass assignments to rc.cmap and rc.cycle through the Colormap and Cycle constructors.

[lukelbd]

Now that rc settings are validated, this has been implemented. It works by saving the colormap name to the rc dict (necessary since the rc dicts should only contain settings printable to proplotrc files). For example:

pplt.rc.cmap = pplt.Colormap('magma')
print(pplt.rc.cmap)

returns 'magma' rather than a colormap instance. This is ok since colormaps assigned to these settings are also automatically registered.