v0.10: Backup and archiving are functional

This version has been put into production at Resonate, so it does work, but there are a number of major caveats.

* No restore functionality, but the backup directories are consistent Postgres data directories.  You'll need to either uncompress the files or turn off compression in the backup.  Uncompressed backups on a ZFS (or similar) filesystem are a good option because backups can be restored locally via a snapshot to create logical backups or do spot data recovery.

* Archiving is single-threaded.  This has not posed an issue on our multi-terabyte databases with heavy write volume.  Recommend a large WAL volume or to use the async option with a large volume nearby.

* Backups are multi-threaded, but the Net::OpenSSH library does not appear to be 100% threadsafe so it will very occasionally lock up on a thread.  There is an overall process timeout that resolves this issue by killing the process.  Yes, very ugly.

* Checksums are lost on any resumed backup. Only the final backup will record checksum on multiple resumes.  Checksums from previous backups are correctly recorded and a full backup will reset everything.

* The backup.manifest is being written as Storable because Config::IniFile does not seem to handle large files well.  Would definitely like to save these as human-readable text.

* Absolutely no documentation (outside the code).  Well, excepting these release notes.

* Lots of other little things and not so little things.  Much refactoring to follow.