Refactor to extract parsePemCert as a method.

For future reuse extract the parsing of a pem certificate into a
function of its own and call that function where the original code
used to be.
Use a custom KeyInfo handler when signing credential.

By default only the signing certificate is included in the signed XML
document. GENI wants the full chain to be included. ABAC also requires
the KeyValue block. Include both of these with the use of a custom
KeyInfo handler for the xml-crypto library.
Bump version to 0.4
Merge branch 'abac-compat' into develop