[yt-dev] Get rid of hdf5_light_reader and freetype

[Matthew Turk]

Hi all,

One of the biggest pain points in our distribution is linking against
external libraries.  We do this in three places by default:

 * HDF5, for the hdf5_light_reader
 * libpng, for write_png
 * freetype, for freetype_writer

hdf5_light_reader was originally written (by me) something like five
years and change ago, because at the time PyTables was slower than I
wanted.  I've been working on improving IO and found that we can get
nearly the same speed from h5py; when combined with overall
performance improvements in yt-3, this still translates to faster
speeds for very large datasets.  On small to medium datasets, the
performance is not noticeably different.  I'd like to propose that we
stop using hdf5_light_reader, which may result in a slight degradation
of performance for (only) Enzo IO.

Additionally, I don't think *anyone* uses the freetype writer, and I'd
like to remove it.  I'm actually not sure if anyone has ever used it.

I think with these two changes we can likely improve our packaging
situation by a good amount, as hdf5 specifically is the main problem
with distribution in Conda.  These changes would only be in yt 3.0,
and would not affect 2.x.

[+-][01]?

-Matt