Document implicit return value behaviour of cdef functions.

Add setup.py method of setting compiler directives

reference naming conflict resolution from C++ wrapping doc, show how to wrap C++ objects in cdef class attributes

Add max_load_factor getter and setter for std::unordered_map.

This might be useful for controlling memory usage at the expense of collision probability.

fix crash with starred assignments where IndexNode generated for type inference ended up being visited

extend array assignment test to include unpacking and starred assignments (even though it's currently highly inefficient)

be a bit smarter about the item index during type inference of indexed slices to allow for better type inference of non-homogeneous containers

make item types of tuple/array unpacking inferable and institutionalise the IndexNode creation for the inference

(Seems we're missing tests...)

clean up recent incorrect change in Symtab code that validated the property generation for extension type attributes