Allow compile output to be either a zip or dir

When passing a directory to compile using --zip or --dir, the -o flag
had to represent a zip file the compiled contents would be written to.
Now, if the path specified by the -o flag is a directory, the compiled
files will be written to the directory rather than erroring out.

Also when passing files to compile as file arguments, the -o flag had to
represent an existing directory. Now, if the path is not an existing
directory, the compiled files will create a zip file at the path that
contains the compiled files.

Test: manual
Change-Id: I92a8e124d53cdb653eb3a7ec549f09f9ad0ef04f