This enables:
* Multiple filters in the main panel and strace etc. views
* Multiple search terms
The search terms are separated by "|" and are still fixed strings
matched case-insensitive.
Added a multi flag at request of BenBE.
Code that is shared across some (but not all) platforms
is moved into a 'generic' home. Makefile.am cleanups to
match plus some minor alphabetic reordering/formatting.
As discussed in https://github.com/htop-dev/htop/pull/553