Deprecated features aren't tested.

Adjusted its API through a deprecation path according to the DEP.

This aligns the Django Template Engine API with the common template
backend API.

It wasn't documented and it wasn't used anywhere.

It wasn't documented and it wasn't used anywhere, except in a few tests
that don't test it specifically and can be rewritten with get_template.

This commit changes the return type of these two functions. Instead of
returning a django.template.Template they return a backend-specific
Template class that must implement render(self, context).

i18n is left aside for now.

Since this package is going to hold both the implementation of the Django
Template Language and the infrastructure for Multiple Template Engines,
it should be untied from the DTL as much as possible within our
backwards-compatibility policy.

Only public APIs (i.e. APIs mentioned in the documentation) were left.

The shorter name is just as explicit and, well, shorter.

Refs #7261 -- Made strings escaped by Django usable in third-party libs.

The changes in mark_safe and mark_for_escaping are straightforward. The
more tricky part is to handle correctly objects that implement __html__.

Historically escape() has escaped SafeData. Even if that doesn't seem a
good behavior, changing it would create security concerns. Therefore
support for __html__() was only added to conditional_escape() where this
concern doesn't exist.

Then using conditional_escape() instead of escape() in the Django
template engine makes it understand data escaped by other libraries.

Template filter |escape accounts for __html__() when it's available.
|force_escape forces the use of Django's HTML escaping implementation.

Here's why the change in render_value_in_context() is safe. Before Django
1.7 conditional_escape() was implemented as follows:

    if isinstance(text, SafeData):
        return text
    else:
        return escape(text)

render_value_in_context() never called escape() on SafeData. Therefore
replacing escape() with conditional_escape() doesn't change the
autoescaping logic as it was originally intended.

This change should be backported to Django 1.7 because it corrects a
feature added in Django 1.7.

Thanks mitsuhiko for the report.

mark_safe and mark_for_escaping should have been kept similar.

On Python 2 this change has no effect. On Python 3 it fixes the use case
shown in the regression test for mark_for_escaping, which used to raise
a TypeError. The regression test for mark_safe is just for completeness.

Thanks zimnyx for the report and Simon Charette, Tim Graham for
the reviews.

Added functions and tests
Added docs and more tests
Added TextField converter to mysql backend
Aliased Value as V in example docs and tests
Removed unicode_compatible in example
Fixed console emulation in examples

sqlall will be removed in Django 1.9, so now's a good time to remove
its usage where it's not important.

Initial SQL data will be removed in Django 1.9 so changes to it
aren't relevant.

Co-Authored-By: Rocky Meza <rmeza@fusionbox.com>

Thanks Mithos for the report and patch.

Refs #23866.