Add some words about pcp-htop to the main man page, and add a
new man page describing the pcp-htop configuration files that
allow new meters and columns to be defined at runtime.
Reasoning:
- implementation was unsound -- broke down when I added a fairly
basic macro definition expanding to a struct initializer in a *.c
file.
- made it way too easy (e.g. via otherwise totally innocuous git
commands) to end up with timestamps such that it always ran
MakeHeader.py but never used its output, leading to overbuild noise
when running what should be a null 'make'.
- but mostly: it's just an awkward way of dealing with C code.
Use configure.ac to handle platform differences where some
build hosts have only a python3, or only python, binary.
Related to https://github.com/htop-dev/htop/pull/6
