BLD: fix the setup.py build_sphinx command

This is perhaps the easiest way to build the documentation, so it's good
to have it working.
DOC: document the build_sphinx command
MAINT: setup.py: point test suite to nose, so that 'setup.py test' works
MAINT: remove setup*egg*.py -- always use setuptools, if present
MAINT: add all source files to MANIFEST.in

sdist with setuptools doesn't play along with source files generated
from Numpy's templates, so they need to be included manually.
BUG: setup.py: pass non-prefixed scipy path to cythonize, but set cwd

This ensures cythonize.dat doesn't depend on cwd. This fixes the build
on pip when Cython is not installed.
MAINT: include everything in MANIFEST.in
MAINT: add more to ignore in MANIFEST.in
DOC: update doc/README.txt
MAINT: setup.py: disable Cython regeneration for released versions
Merge pull request #454 from pv/setup-cleanups

MAINT: setup.py cleanups and additions