Install script ignores arguments to -p option.

[junkyardsparkle]

I just made a Slackware build script for this project, and in the course of doing so noticed that the argument to the -p option described in the install.sh usage is never actually used; if the option is used, the prefix is always determined automatically regardless of argument.

[jepler]

[I'd rather burn down install.sh and make this set up & run via modern Python packaging methods e.g., pyproject.toml & pip install]