Initial addition of the half precision code.

This was downloaded from
https://code.google.com/p/cellperformance-snippets/
Initial working version of half precision.
Tidied and added half floats to tests.
Added tests for floating point types.
Added crude fix for half-precision infinity bug.
Full resolution of inf + clarification of NaNs.

Half precision infinities are now correctly handled and follow
the semantics from numpy. This commit also clarifies the situation with
NaNs. We do not accept NaNs as valid input to the table, which
simplifies  the handling of missing values. It may be possible to
support NaNs as input and to keep the missing value semantics, but it's
problematics. This is at least correct.
Added further test cases and found more problems.
Initial addition of numpy halffloat files.

No modifications made at this point. These files were copied from git
https://github.com/numpy/numpy
on 2013-07-21.
Integrated Numpy half float code successfully.

The numpy code is preferable to the half code for several reasons.
Firstly, it is part of a respected and maintained project, so likely
to be well tested. It is also much easier to read and follow.
Numpy is licensed under a BSD license, so there should be no issue
with including it here.
Removed half code from cellperformance-snippets.
Reverted indentation to original.
Removed memcpys using the union trick.
Reenabled insertion of NaNs and tided up missing.
Improved floating point tests and docs.
Merge branch 'master' into half-dev
Removed dev.py file and bumped to beta 2.