Python2's weird comparison semantics are inconsistent with what
we expect when `NotImplemented` is returned.

If the arrays do not have the same shape then we return NotImplemented.

A new method `object_size` is added to the Array template class, which
calculates the total size of the Python object in bytes.  The function
`size_of` then wraps this method and provides the necessary interface
for a Python method object.

This makes it fail for Python 3 also on 64 bit platforms.

The motivation behind this change is to allow keeping Tinyarray
distributions in git repositories that have a different layout from the
canonical Tinyarray git repository.  This is useful for example for
packaging.

The static version is now kept in the file "version" and can take a
special value that signifies that the version should be determined using
git.  This file is rewritten upon creation of a source distribution.

Also, be explicit about Python 2 support. Drop development
status to 4 - Beta until we can test on other platforms.

In Python 3 changes the semantics of the `/` operator for integers.
See https://docs.python.org/3/howto/pyporting.html#division
for details. This required that we convert Array<long> to Array<float>
before doing the division

There were several changes in hashing between Python 2 and 3,
including several macros being added to avoid "magic numbers".
In addition, instead of having a hand-rolled implementation of
hashing for `double` values we just use the Python API function
`_Py_HashDouble` for compatibility.

There is no `PyUnicode_AsString` in Python 3, so I have no idea
why this even compiled.

Ran 2to3, removed conditional cPickle import and replaced `div`
operation with `truediv`.

We provide no `bf_releasebuffer` member because a buffer is
just a view and has no resources associated with it (other
than those which are handled by Python).

the HAVE_NEWBUFFER flag was only needed in Python 2.x to maintain
compatibility with versions earlier than 2.6, for which the buffer
protocol was not backported. CHECKTYPES is now the default in Python
3.x. Neither of these macros is defined in Python 3.x

Mostly change string -> unicode, except in one instance where we
want to have bytes (pickling/unpickling)

Python 3 only defines floor_divide and true_divide, where
true_divide should return floats even if the two inputs are
integers. This is a non-trivial change, so we disable division
of two integer arrays for now.

Followed http://python3porting.com/cextensions.html#changes-in-python
to convert references to PyInt to PyLong

Followed the advice here
http://python3porting.com/cextensions.html#module-initialization
on porting module creation. Should remain compatible with
Python2 this way.