Move the logging of the WA version and command line used to invoke it
from run command into main() inside entrypoint. That way, these will be
the first entries in the log file, now that early log records are no
longer lost.
Add support for "~~" special value that indicates that, when merging
into another set, all values from that set should in fact be dropped.
Apart from the unique merge semantics, "~~" just like any other "~"
value.
--diable can now be used to disable both intruments and
result_processors from the command line (overriding configuration
files). Rename variable names to reflect this.
Changing the way target descriptions work from a static mapping to
something that is dynamically generated and is extensible via plugins.
Also moving core target implementation stuff under "framework".
