Add 'control' module to the list exported by usb package.

'control' was not in the __all__ field for the 'usb' package. This means that
  from usb import *
  control.XXX
would fail to find the module 'control'.
Merge pull request #50 from callpraths/add_control_to_all

Add 'control' module to the list exported by usb package.
Fix array creation on Python 3.4.

On Python 3.4, you cannot mix 'B' typecode with str. We use a tuple
instead for compability with older versions of Python.

closes #51.
Fix performance regression.

Commit 01b5d9e6 introduced a performance regression: creating a tuple of
zeros is much slower than a string. For Python 2 we have to use
'\x00' * length, but for Python 3 we need b'\x00' * length.

We use a little dirty hack with encode('utf-8') method to keep
compatibility between Python 2 and 3.
Merge remote-tracking branch 'walac/pyusb/master'