Valuta

- Add basic SQLAlchemy support.

- Suppress weirdest bug with a strange character ``\xa0`` appearing when
using template tags without providing a locale on GitHub actions (locally
everything passes without the bug).

This release is somewhat incompatible with previous versions for what's
related to the displaying value in currency units (using any
``display_in_currency_units`` or shortcuts). If you want old behaviour,
add ``format=DISPLAY_FORMAT_NUMBER`` to places where you used
``display_in_currency_units`` method or a correspondent shortcut function.


- Add ``locale`` and ``decimal_quantization`` args to the ``format_currency``
everywhere.
- Do not provide a default value for ``format`` (follow the ``babel`` defaults
approach).

- Added `valuta.contrib.django_integration.context_processors.constants``
context processor module.
- Documentation improvements.

- Added `display_in_currency_units` method, `shortcuts` module function and
a magic method to the Django integration package, as well as the template
tags library.

- Minor fixes in the Django app (for Django 2.2).