`revng.api` now autodetects files (libraries, pipeline yamls) for
initialization via the same mechanism used by `revng.cli`. This removes
the need to pass them via environment variables from `revng daemon`
and allows easy interaction with python's C API.
Fix termination of the daemon process during test, previously it was the
daemon instances were not cleaned up properly and remained running after
the tests
We used to collect all binaries into the `bin/` directory. However this
led to confusions since certain commands where available both as
`revng-command` and `revng command`.
This commit moves all the executables except `revng` into
`libexec/revng`, which, according to FHS, is dedicated to "internal
binaries that are not intended to be executed directly by users or shell
scripts".