This commit fixes command line parsing of revng through the
REVNG_OPTIONS environment variable. Previously the env was prepended to
the actual command-line variables, now it's appended, allowing to
specify command line arguments that depend on `-load`s.
Package revng's python code in two wheels: `revng` and `revng_internal`.
The revng wheel contains the
`revng.{pipeline_description,model,tupletree}` modules, while the
`revng_internal` one everything under `revng.internal`.
Ivan Krysak