These limits can cause errors in some environments, e.g. Docker in Docker on Mac M1.
Entirely remove limits from the build, s3, and azure hosts since memory usage on these hosts is out of our control and not useful for testing.
Also allow empty variables to be rendered as blank.
Command-line help is now generated at build time so it does not need to be committed. This reduces churn on commits that add configuration and/or update the help.
Since churn is no longer an issue, help.auto.c is bzip2 compressed to save space in the binary.
The Perl config parser (Data.pm) has been moved to doc/lib since the Perl build path is no longer required.
Likewise doc/xml/reference.xml has been moved to src/build/help/help.xml since it is required at build time.
This is consistent with the way BackRest and BackRest test were renamed way back in 18fd2523.
More modules will be moving to pgBackRestDoc soon so renaming now reduces churn later.
