Expressions such as <REPO:ARCHIVE> require a stanza name in order to be resolved correctly. However, if the stanza name is passed to the remote then that remote will only work correctly for that one stanza.
Instead, resolved the expressions locally but still pass a relative path to the remote. That way, a storage path that is only configured on the remote does not need to be known locally.
Prior to this the Perl remote was used to satisfy C requests. This worked fine but since the remote needed to be migrated to C anyway there was no reason to wait.
Add the ProtocolServer object and tweak ProtocolClient to work with it. It was also necessary to add a mechanism to get option values from the remote so that encryption settings could be read and used in the storage object.
Update the remote storage objects to comply with the protocol changes and add the storage protocol handler.
Ideally this commit would have been broken up into smaller chunks but there are cross-dependencies in the protocol layer and it didn't seem worth the extra effort.
This is a complete protocol client implementation in C.
Currently there is no C server implementation so the C client is talking to a Perl server. This won't work very long, though, as the protocol format, even though in JSON, has a lot of language-specific structure. While it would be possible to maintain compatibility between C and Perl it's probably not worth the effort in the long run.
Just as in Perl there are helper functions to make constructing protocol objects easier. Currently only repository remotes are supported.
