Absql

Functions are as filters. For example:

python3
from absql import Runner as r

def case_it(x):
return x.upper()

r.render_text("hello {{person | case_it}}", person="you", case_it=case_it)
'hello YOU'

- Adds `partial_kwargs`: a list of function kwargs to partialize. This was previously hard-coded as `engine`, but can now be set by the user.

- Updates tests and built-in functions to be SQLAlchemy 2.x-compatible.

- Moves `render_[x]` functions to a submodule.

clean_spacing` always adds a single space in Jinja references.

Files without frontmatter can start with `{`.

render` method of instantiated runner accepts `extra_context`

Handles [null type](https://yaml.org/type/null.html) in YAML constructors.