Bug and fix reported by Mark Lodato.

Add a target (with alias "html") to build README.html from README.txt
using rst2html.  This is not run by default.

The only reason I had a "rst" extension was so that GitHub would pick it
up.

--HG--
rename : Demos/freeze/README.rst => Demos/freeze/README.txt

Add an example of building a --pymain Python interpreter to the README
and to the Makefile.

Add an option to build a regular interpreter, calling Py_Main(), rather
than running the first module as __main__.

Instead of hard-coding the compiler flags and libraries, extract them
from distutils.sysconfig.

I mis-spelled "combinatorics", and I forgot to use the -c flag to gcc.

--HG--
rename : bin/cython_freeze.py => bin/cython_freeze

The files originally had README.rst in the top level and the examples in
the example directory, but now all are in Demos/freeze.

The PyInt conversion functions generate two warnings when compiled under
`gcc -Wall -Wextra`:

1. comparison of unsigned expression < 0 is always false

2. signed and unsigned type in conditional expression

This patch fixes these problems by creating a new temporary variable
`is_unsigned`, which fixes problem 1, and by converting the ternary
return expression into a normal if/else branch, which fixes problem 2.

--HG--
extra : rebase_source : 3512ea980463bae13f30b0d8bd395cabe253e65c

--HG--
extra : rebase_source : 37bb9de5574e1f7b4f288192eaa3c70a2ae350ca

This provides a fast way to check to see the data type of an ndarray.
For example, to check to see if an integer is 64 bits:

    PyArray_TYPE(a) == NPY_UINT64 or PyArray_TYPE(a) == NPY_INT64