More separation of the protocol and remote layers than was done in issue #106.
Settings are passed to the remote via command-line parameters rather than in the protocol.
* IMPORTANT NOTE: This flag day release breaks compatibility with older versions of PgBackRest. The manifest format, on-disk structure, and the binary names have all changed. You must create a new repository to hold backups for this version of PgBackRest and keep your older repository for a time in case you need to do a restore. The `pg_backrest.conf` file has not changed but you'll need to change any references to `pg_backrest.pl` in cron (or elsewhere) to `pg_backrest` (without the `.pl` extension).
* Add info command.
* More efficient file ordering for backup. Files are copied in descending size order so a single thread does not end up copying a large file at the end. This had already been implemented for restore.
* Logging now uses unbuffered output. This should make log files that are being written by multiple threads less chaotic. Suggested by Michael Renner.
* Experimental support for PostgreSQL 9.5. This may break when the control version or WAL magic changes but will be updated in each release.
* Includes updating the manifest to format 4. It turns out the manifest and .info files were not very good for providing information. A format update was required anyway so worked through the backlog of changes that would require a format change.
* Multiple database versions are now supported in the archive. Does't actually work yet but the structure should be good.
* Tests use more constants now that test logs can catch name regressions.
* Fixed an issue where archive-copy would fail on an incr/diff backup when hardlink=n. In this case the pg_xlog path does not already exist and must be created. Reported by Michael Renner
* Allow duplicate WAL segments to be archived when the checksum matches. This is necessary for some recovery scenarios.
* Allow comments/disabling in pg_backrest.conf using #. Suggested by Michael Renner.
* Better logging before pg_start_backup() to make it clear when the backup is waiting on a checkpoint. Suggested by Michael Renner.
* Various command behavior, help and logging fixes. Reported by Michael Renner.
* Fixed an issue in async archiving where archive-push was not properly returning 0 when archive-max-mb was reached and moved the async check after transfer to avoid having to remove the stop file twice. Also added unit tests for this case and improved error messages to make it clearer to the user what went wrong. Reported by Michael Renner.
* Fixed a locking issue that could allow multiple operations of the same type against a single stanza. This appeared to be benign in terms of data integrity but caused spurious errors while archiving and could lead to errors in backup/restore. Reported by Michael Renner.
* Replaced JSON module with JSON::PP which ships with core Perl.
ASSERTs still dump stack traces to the console and file in all cases. ERRORs only dump stack traces to the file when the file log level is DEBUG or TRACE.
* Better resume support. Resumed files are checked to be sure they have not been modified and the manifest is saved more often to preserve checksums as the backup progresses. More unit tests to verify each resume case.
* Resume is now optional. Use the `resume` setting or `--no-resume` from the command line to disable.
* More info messages during restore. Previously, most of the restore messages were debug level so not a lot was output in the log.
* Fixed an issue where an absolute path was not written into recovery.conf when the restore was run with a relative path.
* Added `tablespace` setting to allow tablespaces to be restored into the `pg_tblspc` path. This produces compact restores that are convenient for development, staging, etc. Currently these restores cannot be backed up as PgBackRest expects only links in the `pg_tblspc` path.
