Added a note about iOS7 seeming to have issues with PKCS#12 without the
password embedded
Forgot "package main"
Check for attempts to access invalid payload keys
Implement exportable()
Add the test suite for common payload code
Change release status to testing
Add points for working with Storable, and testing that
Redefine the Data type to only return plain filehandles

We also make sure that the open handle can read and seek, as well as
stripping off any tied object (like IO::File).
validate_data should unconditionally return undef at the end
Implement test suite for data.

Closes #5.  Still need to test with write-only and un-seekable handles.