Various users want automatic demo recording. Add new command line options:
-auto-record-demo start recording on level entry
-record-demo-format set demo name automatically
For -record-demo-format, specify a template containing any mix of strftime
insertions, variable insertions, and literal text. As a special case, specify
"." to use the builtin template "%Y%m%d.%H%M%S-$p-$m". Most users should use
".". Supported variables:
$p name of pilot recording the demo
$m name of msn/mn2 file played
Suggested by jeffersoncarpenter in https://github.com/dxx-rebirth/dxx-rebirth/pull/33, but implemented by vLKp.