added mapping stanza for regular files

When nexe is invoked with regular files as arguments, map these as regular files inside zerovm sandbox too

Ex.
When running:
$ zvsh cat.exe @file.txt

The mapping section in nvram will contain:

[mapping]
channel=/dev/1.file.txt,mode=file
Merge pull request #24 from pkit/add_mapping

added mapping stanza for regular files