Add context manager for managing font properties

[vinisalazar]

Hi @erdogant,

I came up with this potential solution for #3 which only adds one line (269). The other changes are merely an indent to bring the code block inside the context body.

However, I would go one step further and add an argument to this function allowing to set the font family. I can add it to this PR, or open a new one. If these are merged, I can also see about incorporating the changes into the scatterd calls in the pca package.

Let me know what you think.

Thank you,
Vini

Summary of changes

• In function _set_font_properties, use matplotlib.rc_context()

This resets the rcParams upon leaving the context body, which prevents the parameters set here
from interfering with the rest of the figure.