Fix msvc compiler warning C4244

warning C4244: 'initializing': conversion from 'double' to 'float', possible loss of data

Clean up insertion points after use in prange code since they conflict with the deep-copying that with-statements use for their finally-clause.
Closes GH-2780.

Avoid useless "div by zero" checks in optimised constant division code. Also avoid using a (named) C macro where code generation will do.
See GH-2820.

Fix exception messages for float division by zero, as well as their tests (which were wrong in Py2.6).

Closes #2820.

Remove superfluous code

Simplify logical expression

Fix casting ssize_t to unsigned

See #2818.

Pointer buf cannot be NULL

Clarify that extension types which implement "__cinit__" do not require their base types to implement it.
Closes #2809.

Speed up multiplication of Python numbers with small integers (<= 2**30)

Special-case some arithmetic operations with 0 that can be implemented without creating new objects.

Speed up &-ing multi-digit PyLongs with known single digit integers, e.g. "bigx & 255" or "bigx & 1".

See #2807.

Closes #1982.