MAINT: use scikit-image wheels collection

An attempt to address Cython build failures.
Mention transport argsort for inverting the transposition
MAINT: add --no-cython-compile flag for Cython

Add flag to prevent Cython compiling itself.  This speeds Cython
installation and doesn't much slow down pyx file building.

From suggestion by Nathaniel.
Merge pull request #5265 from matthew-brett/rackspace-cython

MAINT: use scikit-image wheels collection
ENH: add `multi_dot`: dot with multiple arguments.

`np.linalg.multi_dot` computes the dot product of two or more arrays in
a single function call, while automatically selecting the fastest evaluation
order.

The algorithm for selecting the fastest evaluation order uses dynamic
programming and closely follows:

    Cormen, "Introduction to Algorithms", Chapter 15.2, p. 370-378
DEP: Replaced arr->nd with PyArray_NDIM in fortranobject.c
DEP: replaced arr->nd with PyArray_NDIM in C code generation scripts
DEP: replaced arr->data with PyArray_DATA
DEP: replaced arr->dimensions with PyArray_DIMS(arr) or PyArray_DIM(arr,i)
DEP: Replaced arr->descr, arr->flags and arr->base with the PyArray_* functions
DEP: Using PyArray_SIZE and PyArray_TYPE instead of PyArray_DESCR()->elsize etc
DEP: Using the internal PyArrayObject_fields API for the swap_arrays and dump_attrs functions
DEP: Replaced NPY_[F,C]ARRAY with NPY_ARRAY_[F,C]ARRAY
DEP: Corrected some type errors that appear when enabling NPY_NO_DEPRECATED_API
DEP: Replace NPY_CONTIGUOUS with NPY_ARRAY_C_CONTIGUOUS
DEP: removed deprecated API calls from test code (wrapmodule.c)
DEP: #declaring NPY_NO_DEPRECATED_API in fortranobject.h
Update docstring for multivariate_normal().

The change is to make a stronger statement that the covariance matrix must
be positive-semidefinite and that if it is not, then the results are not
guaranteed across NumPy versions.
MAINT: give up on rackspace wheels

Rackspace wheels (from http://wheels.scikit-image.org) are giving
timeouts, again - e.g.:

https://travis-ci.org/numpy/numpy/jobs/40578751

Use Nathaniel's trick of not compiling Cython, for speed, and to work
round previous Cython build breakage.
Merge pull request #5271 from matthew-brett/give-up-on-rackspace-wheels

MAINT: give up on rackspace wheels