Refactor the `here()` function out for the `pyhere` package

[chendaniely]

Potentially port just the here() function to https://pypi.org/project/pyhere/

I suspect not much will change, but there have been a lot of changes to this package and we want to make it so that the downstream package maintainer has a good + easy time.

[jamesmyatt]

All of the here functionality should already be extracted into the pyprojroot.here module. The only issue is that from pyprojroot import here needs to be deprecated.

[chendaniely]

This issue was mainly a placeholder for pyopensci submission to make the import + use as easy as possible for the end user.

it depends on how much we can get this implementation downstream.

There are 2 ways we can choose to import the here() function:

from pyprojroot.here import here

here()

or

# this requires some extra stuff into the __init__.py file
from pyprojroot import here

here()