Fix git repository version detection for older git versions

retriever: Restore compatibility with perl pre 5.25

Log version when deployed from git repository

README: Minor spelling/wording fixes.

README: Updates for ENDIT v2, TSM renaming, etc

Prometheus stats: Emit HELP strings for all metrics

Misc code clean up

retriever: Cache request info instead of parsing on each iteration

retriever: Reduce logging of ENOENT and broken req files

tsmretriever: Demote Not-doing log messages to debug level

tsmretriever: Silence skip-messages due to remountdelay just after mount

tsmretriever: Clean in dir daily, try 2

retriever: Check free space of in/ directory, not out/

Also export stats as Prometheus text format

retriever: Apply brake when fs fills up

retriever: Gracefully handle incomplete/broken request files