parsemail: Move parsing to 'parser'

parsemail: Move parsing to 'parser'

Separate the parsing of mails from the CLI aspects of parsemail. Since
there is already a 'parser' module, it makes sense to place the parsing
functionality here. This will allow for additional uses of this parsing
functionality in the future.

Signed-off-by: Stephen Finucane <stephen.finucane@intel.com>
Reviewed-by: Andy Doan <andy.doan@linaro.org>