retsnoop v0.4-alpha

retsnoop: add ability to log stacks with duration longer than specified

Allow to request capturing only those stacks for which entry function was
executing for at least specified about of milliseconds. Use '-L 123' to
request logging stacks that took at least 123ms. Most probably will be used
with --success-stacks (-S), but should work with error-only stacks as well.

Along the way fix annoying issue of emitting one extra unnecessary and
duplicate intermediate stack.

Plus success stacks should have better stack traces now.

Also cleaned up usage string.

Signed-off-by: Andrii Nakryiko <[email protected]>

retsnoop v0.3-alpha

retsnoop: report real clock timestamp

Signed-off-by: Andrii Nakryiko <[email protected]>

retsnoop v0.2-alpha

retsnoop: allow @file-with-globs.txt feature

Signed-off-by: Andrii Nakryiko <[email protected]>

retsnoop v0.1-alpha

Initial alpha pre-release.