PR Summary

Dynamically generate pyplot functions at import time. Functions define a proper__signature__ (via thefuncsigs backport on Py2, which is a new dependency).

This PR does not appear to cause slowdown in the import time, as shown by

import sysfrom time import perf_counterfor _ in range(10):    start = perf_counter()    import matplotlib.pyplot    stop = perf_counter()    print("elapsed: {}ms".format(int((stop - start) * 1000)))    for mod_name in list(sys.modules):        if mod_name.startswith("matplotlib"):            del sys.modules[mod_name]

hold functionality was removed from the pyplot functions (it is scheduled for removal anyways) to avoid a needlessly complex implementation.

Remove boilerplate.py, which becomes unused.

Dynamically generate some more functions (plt.axis,plt.clf, etc.) which actually fall into the same pattern. Fix their docstrings accordingly.

[As a side note, some profiling suggests that right now the slowest step at import time is by far the calls to the various checkdep_* if you happen to have theps.usedistiller ortext.usetex rcparams set.]

PR Checklist

• [OK] Has Pytest style unit tests (well, if the current test suite still pass)
• [OK] Code is PEP 8 compliant
• [N/A] New features are documented, with examples if plot related
• [N/A] Documentation is sphinx and numpydoc compliant
• [?] Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there) (not clear if needed (hold also needs to be removed from the Axes class itself, this can be the object of a separate PR and documented there))
• [N/A] Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way