Add day formatting

[philchalmers]

I would like to add pbapply as a dependency to one of my packages (specifically after the a version which supports parallel computations is released to CRAN). However, I was wondering if you could add a days formatting to the progress output. Some of my apply statements could take days to finish, therefore I would prefer to print the number of days and hours instead of just the hours alone.

The following pull request gives this type of output:

> getTimeAsString(60)
[1] "01m 00s"
> getTimeAsString(60 * 60)
[1] "01h 00m 00s"
> getTimeAsString(60 * 60 * 24)
[1] "01d 00h 00m 00s"
> getTimeAsString(60 * 60 * 24 * 4)
[1] "04d 00h 00m 00s"
> getTimeAsString(60 * 60 * 24 * 4 + 1)
[1] "04d 00h 00m 01s"

[psolymos]

Thanks @philchalmers , this looks like a useful extension.