Re-write encryption script using simplified interface

Hi,

The encrypt script didn't work for me (testing on Fedora 19 with ruby 2.0.0p247 (2013-06-27 revision 41674) and gpgme (2.0.2) so I re-wrote it using the simplified crypto interface [1]

It now works just fine.

The decrypt script worked fine without modification

[1] http://www.ruby-doc.org/gems/docs/b/benburkert-gpgme-0.1.5/GPGME/Crypto.html