* Return the error code specified by errno if select fails. API change, slated
  for 0.5.
* Replace Timeout datatype with Maybe CTimeval. API change, slated for 0.5.
* Move the select EINTR retry code from C to Haskell. Separate out clock_gettime
  into a package of its own. Slated for 0.5?
* Reorder functions to make the documentation more logical.
* Move CTimeval, probably into a package of its own.