timestamp

@bendem wrote a program like this in C++, so I wanted to write my own version in Rust for funsies.

Default format is %c, but you can change it by passing in any arg.

sh % {echo 'Hi'; sleep 2; echo 'Hi again'} | timestamp [Sat Aug 6 17:04:57 2016] Hi [Sat Aug 6 17:04:59 2016] Hi again

sh % {echo 'Hi'; sleep 2; echo 'Hi again'} | timestamp '%S' [11] Hi [13] Hi again