Display OIDs in dotted form

This commit causes `repr` for OIDs to display the OID in dotted
form instead of as the raw ASN.1 BER-encoded bytes.

Also-Authored-By: Simo Sorce <simo@redhat.com>
Support constructing OIDs from integers

This commit introduces support for constructing OIDs using integers
(instead of having to pass the BER-encoded bytes to the constructor).