Keep texture pixel data as pointer to array of proper type.

Memory would leak when the destructor of std::unique_ptr<GLvoid> wouldn't delete
the array properly.
Initialize widget placement in Widget contructor.

Others may depend on this data not being garbage even before the first layout.
Allow nanaka to be built as a single threaded application.

This is a bit hackety, but the threading needs to be ripped out and replaced
anyway, so this will do for now.
Add GYP option for determining library type to be built.
Add zlib external library.

For platforms lacking a prebuilt version of it.
Add support for a new target platform; the web!

This allows nanaka be compiled to javascript or asm.js using emscripten, then
run in any modern web browser.
Update README.
Increase minimum length of buffer for audio playback.

Web browsers are unhappy with short audio buffers and end up making hostile
clickety sounds.