Brief parameter for humanize function

## Feature Request

This parameter is False by default. When true, it shortens the date and time terms. For example:
```
>>> present = arrow.utcnow()
>>> shift = present.shift(hours=2, minutes=34, seconds=56)
>>> shift.humanize(present, brief=True, only_distance=True)
>>> 2h 34m 56s
```

Start at the Python humanize function entry point and trace how its date and time terms are currently formatted. Add the optional brief behavior described in the issue, preserving the default output, and verify the example produces shortened terms such as 2h 34m 56s.

Written by the indexing model from the issue text.