Updated astropy-helpers to v0.4.2
Merge pull request #46 from astrofrog/update-helpers

Updated astropy-helpers to v0.4.2
Initial implementation of speedup attempts, including parallel implementations.
C version of the reproject routine, including the parallel one.
Attempt at fixing the Travis failures related to documentation and Python 2 vs 3.
More Python 3 fixes.
Python 3.4 enforces K&R C style, account for that.
Temporarily enable the selection of the method and number of cores to use
from the high level routine.
New implementation that uses cython for setting up the arrays,
and raw C for the computation.
Revert "Temporarily enable the selection of the method and number of cores to use"

This reverts commit d3866211578d1a21b74dbd34a5f3831558cc4025.
Tentative workaround for the egg_info travis failures.
Fix the previous fix: don't import numpy at all for egg_info.
Move ilon/ilat/olon/olat inside the C function as local variables.
Move the declaration of the static arrays at the top of the function.
First round of cleanup. Just leave the old implementation for reference.
More cleaning: now use a static pool of workers created at module import,
and put options common to the serial and parallel implementations in
a shared list.
Fix the offset-by-0.5 bug in both the Python and C routines, and add a way
to select the number of processes to use in the parallel implementation.

Docs were added as well.
Move the pool management back into the main function,
and add code to handle gracefully ctrl+c while running
things in parallel.
Invert the order of a comparison to account for the fact
that in Python 3 None is not comparable to ints any more.
Fix for the handling of array sizes. We were assuming that all the input arrays
had the same shapes, but actually they could differ.