Pyjams

* Use `text2plot` in `abc2plot` and `signature2plot`.
* Better handling of linebreaks in Matplotlib and LaTeX mode in `str2tex`.
* Added `text2plot`, adding text onto a plot.
* Added `int2roman` and `roman2int`, converting integer to and from
Roman literals.
* Combine `abc2plot` and `signature2plot` in one file `text2plot.py`.
* Added `abc2plot`, adding a, B, iii), etc. onto a plot.
* Added `signature2plot`, adding a copyright notice onto a plot.
* Added 'pyjams_color.pdf' as reference to available colormaps.

* Added tests for `color`.
* Added 'pragma: no cover' to plot and MPI sections of codes so that they
are not included in coverage report.
* Cleaned mcPlot docstrings.
* Cleaned formats in all docstrings.
* Added current colors of Paul Tol, i.e. sron color palettes.

* Add `position`, which positions arrays of subplots to be used with
Matplotlib's add_axes.

* Write standard output file of mcPlot into current folder.
* Add `str2tex`, converting strings to LaTeX strings
* Bug in masked array input to `alpha_equ_h2o`, needed to check masked array
before ndarray because the former is also the latter.
* Enhanced tests of `alpha_equ_h2o`, `alpha_kin_h2o`, `fit_functions`,
`argsort` so that have 100% coverage.
* Added `color`, a collection of color palettes and continuous color maps.

* Add `mcPlot`, the standard plotting class of Matthias Cuntz.
- It currently assumes that MyriadPro is installed for LaTeX if one
wants to typeset with latex (-u, --usetex). For installing MyriadPro
on macOS see https://github.com/mcuntz/setup_mac#myriad-pro This
should be similar on Linux.
- There are no tests for mcPlot yet.

* Avoid overflow warnings in `alpha_equ_h2o`.
* Added `alpha_kin_h2o`, kinetic fractionation factors for molecular
diffusion of water isotopologues.