FRQ: simplify how to set the plot style in plot.style()

[kay-ro]

Proposed new feature or change:

The call of the amep.plot.style() function is different for whether the goal is to set an amep style or the default matplotlib style. To make this functionality more user-friendly, the labels for the styles can be simplified and one added for the default matplotlib style.
The following changes would simplify the usage:

• "amep_latex" -> "latex"
• "amep_standard" -> "standard"
• mpl_default=True -> "matplotlib"

When updating the code in compliance with a minor release, please keep it backwards-compatible.
Additionally, prepare for a major release with the simplified call arguments by adding a note to the documentation:

.. note:: Deprecates in 2.0.0
          `mpl_default` will be removed in an upcoming major release. Please use "matplotlib".
          "amep_latex" and "amep_standard" will be removed. Please use "latex" and "standard" instead.