Also improve the documentation for operators in general.

special methods are not included by autodocs by default, and
as class documentation pages are generated by autosummary,
we cannot just explicitly include __call__. We get around this
by using a custom autosummary template for the operator classes.

For cython extension modules, the method signature for __call__
is still not embedded properly.
See https://github.com/cython/cython/issues/1577.

This patch fixes the reasons for compiler warnings in
 - partitioner (signed unsigned comparison),
 - graph/util (maybe uninitialized),
 - operator (maybe uninitialized).

Add tests to make sure we explicity check for `sum == True`

This reverts commit e34b4b73.

Previously, calling an operator would spuriously return a float
when the operator was hermitian, even if the bra/ket vectors
sandwiching the operator were not the same.

Explicitly initialize pointers to NULL, refrain from using
pythonic constructs, e.g. `a or b`, with cython extension types;
this causes cython to produce (correct) code where pointers are
not cast to the correct type.

Viacheslav Ostroukh authored 8 years ago and Christoph Groth committed 8 years ago

    Fixes issue #74

Without this measure, a failed check is no longer detected.  This seems
to be a bug in gitlab CI.