* Don't restrict the list of compatibility values to check against
to only those we have mapped, also support unmapped more exotic
ones.
* Allow 1:1 check against sys.platform values (with startswith).
Combined with the above that allows very granular compatibility
modelling ("freebsd11", "freebsd12") if required.
* Instead of only whitelisting ("linux", "freebsd") now also black
listing is possible ("!windows").
A detected os must match all provided whitelist elements (if the
whitelist is empty that is considered always the case) and none of
the backlist elements (if the blacklist is empty that is also
considered always the case).
See the included unit tests for examples of how this works.
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