Change points_in_polygon to return boolean array

[corranwebster]

Fixes #237.

Using unsigned char for boolean array rather than int.

[jwiggins]

Why use unsigned char and not bool?

[corranwebster]

Are we guaranteed bool* is an array of bytes? My knowledge of C++ isn't deep enough to know if that's certain.

[jvkersch]

Are we guaranteed bool* is an array of bytes?

I heard you guys talking about this at lunch and I was curious myself, so I looked it up in the C++ standard, and it's not guaranteed. Edit: cf. section 5.3.3 of this, in particular footnote 75.

[jwiggins]

Right... I can't find a link to the relevant part of the C++ standard, but I did find this: http://en.cppreference.com/w/cpp/language/types

So no, it's not necessarily an array of bytes. Is this then dictated by what the Numpy C-API expects (even if obscured by SWIG)?

[jwiggins]

I say use whatever Numpy expects. That's probably unsigned char. If so, LGTM.

[corranwebster]

Yep - it's because numpy expects a bool array to be an array of bytes in memory with 0 and 1 values. So signed vs. unsigned shouldn't matter, I guess, but unsigned makes it clearer that we're just getting a chunk of memory.