MAINT: merge scalarmathmodule into umath module

There is no good reason it needs to be its own module.
Also removes the undocumented pymath alter/restore functions.
DOC note the effect of #1866 in byteorder discussion
ENH: support parallel compilation of extensions

Allow extensions using numpy.distutils to compile in parallel.
By passing `--jobs=n` or `-j n` to `setup.py build` the compilation of
extensions is now performed in `n` parallel processes.
Additionally the environment variable NPY_NUM_BUILD_JOBS is used as
the default value, if its unset the default is serial compilation.

The parallelization is limited to within the files of an extension, so
only numpy multiarraymodule really profits but its still a nice
improvement when you have 2-4 cores.
Unfortunately Cython will not profit at all as it tends to build one
module per file.
DOC: update installation instructions
DEP: deprecate pkgload
MAINT: warn instead of raise
Merge pull request #5245 from argriffing/deprecate-pkgload

DEP: deprecate pkgload
Fix issue with fromarrays not correctly determining a format string for unicode data (in the process eliminate some unnecessary cruft)
Merge pull request #5251 from embray/astropy-3052

Issue with fromarrays not using correct format for unicode arrays
Merge pull request #5161 from juliantaylor/parallel-distutils

ENH: support parallel compilation of extensions
BUG: fix header using symbols not available in py3

Inside numpy we handle this via the py3kcompat header which is not
really public api. So for our public headers we need some explicit
checks.
Merge pull request #5257 from juliantaylor/py3-header-fix

BUG: fix header using symbols not available in py3
MAINT: use scikit-image wheels collection

An attempt to address Cython build failures.
Mention transport argsort for inverting the transposition
ENH: added std::complex support to numpy.i

numpy.i now includes ready-made typemaps for std::complex<float>
and std::complex<double> .  Tests were added to testArray using
a newly defined ArrayZ class.
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