Inline keyword for cdef functions, variable assignment on declaration (+optimization)

Inline keyword for cdef functions, variable assignment on declaration (+optimization)

"cdef inline foo()" now valid, and will place inline in the resulting c code

"cdef o = expr" and "cdef type x = expr" now valid.
This may not seem like a huge change, but it ended up requiring
quite a bit of work. The variables are still all declared at the
top, but the assignment takes place at the specified line in the
code.

If an assignment is made at declaration, the variable is initalized to
0 rather than None (also skipping an INCREF) and Py_XDECREF is used on
exiting the function (in case an error occured before the actual value
was calculated). Hence these variables MUST NOT be used before they are
defined or it will probably segfault.