Deprecate use of ENV for setting config.

This paves the way for clean parameters, rather than polluting the
environment. log_level is also introduced to the configuration, as ENV
can no longer be used.
Fix missing VERSION require.
Add all configure options to executable.

This makes it possible to configure Redimap entirely from the command
line. Run with `--help` to see options and explanation.
Document command line options, replacing ENV instructions.
Merge branch 'configuration' into develop