Change command line, making input files positional arguments at the end.

- Multiple input files can now be specified.
- By default, file format is guessed from filename extension;
  this guess can be overruled with --filetype (applies to all input files).
- Input files need not be of the same type (CSV, GPX, ESRI Shapefile, etc).
- Wildcard expansion is done on Windows. (On unix, this is normally done
  by the shell; on Windows, apps are expected to handle it themselves.)

We still support the old method of specifying an input file, but log a
deprecation warning. This support will be removed eventually.