BUG: stats.rankdata returned incorrect results for ties with a large number of elements.

Instead of accumulating the ranks of the tied elements, a simple formula is used
for the average rank.
PEP8 tweaks.
REL: change version on master branch to 0.13.0-dev
Merge pull request #436 from WarrenWeckesser/bug-rankdata

BUG: stats.rankdata returned incorrect results for ties with a large number of elements
DOC: fix some warnings + make more plots build with Matplotlib 1.2.0
MAINT: Remove Cython-generated files
BLD: generate sources using Cython at setup.py time
MAINT: include cythonize.dat into source packages

This ensures that Cython files are not regenerated if this is not
necessary. This allows also building without having Cython installed.
MAINT: tools/cythonize: fail late without Cython, use text file instead of pickle as db
MAINT: tools/cythonize: remove support for git
MAINT: include cythonize in sdist
MAINT: ship also _vq_rewrite.c

This file is unused, but include it still in sdist to allow build
without Cython installed.
MAINT: cythonize: normalize db paths
MAINT: tools/cythonize: deal with c++ Cython files
GEN: add all autogenerated .pyx files
MAINT: tools/cythonize: sort hash DB, to make sdist reproducible
BUG: make cythonization build to pass on python 3
BLD: don't require Cython to be installed for each Python version.
Merge pull request #403 from pv/cython-builddep

MAINT: Cython as a build dependency
DOC: minor changes: fix reference formatting, change wording