Previously, it was necessary to support older versions of Python for
compatibility. F-strings were released in Python 3.6. Python 3.5 was
marked as unsupported by the end of 2020, so now it's possible to start
using f-strings safely for better readability and performance.
Access log used for the variables testing instead of limited routing.
Added missed test for $status variable.
Some tests moved from "test_access_log.py" to "test_variables.py".
If you need to specify a $ in a URI you can now use '$dollar' or
'${dollar}'.
Added some tests for the above to test_variables.py setting a Location
string.
In the case that routes or upstreams is empty and the pass option is a variable.
If the resolved pass is routes or upstreams, a segment error occurred.
