Add lsdepth, findtree, cmin, and cmax

[cfhammill]

As discussed in #298

Only issue here is that cmin and cmax need to be done in a MonadIO, so as far as I can tell it can't be used with mfilter with them directly.

Code review would be appreciated, I'm still pretty new to haskell.

[Gabriella439]

Looks good! Just one minor style suggestion

I'm also not that concerned if cmin and cmax have to be in IO, because in the worst case a user can do:

example = do
    file <- findtree somePattern (ls ".")
    True <- cmin someTIme file
    return file

[Gabriella439]

Minor stylistic suggestion: I'd suggest using a non-pointfree function:

cmin t file = adapt <$> lstat file
  where
    adapt x = posixSecondsToUTCTime (modificationTime x) > t

[Gabriella439]

It looks like Travis is failing on older versions of GHC due to Functor not being a super-class of MonadIO. You can fix that by using liftM or do notation

[cfhammill]

Hopefully this is fixed now, the build failed due to the hackage outage.

[Gabriella439]

Yep, that fixed it! Thanks for doing this :)