MEDIUM: sample: implement us and ms variant of utime and ltime

MEDIUM: sample: implement us and ms variant of utime and ltime

Implement 4 new fetches:

- ms_ltime
- ms_utime

- us_ltime
- us_utime

Which are the same as ltime and utime but with milliseconds and
microseconds input.

The converters also suports the %N conversion specifier like in date(1).

Unfortunately since %N is not supported by strftime, the format string
is parsed twice, once manually to replace %N, and once by strftime.