zero buffers in the JavaScript bindings

Poljar's improved python bindings

also reduce the amount of memory copying that we do

since they're not for the right repository any more

- build both Python2 and Python3 libs by default, and add separate rules
  building Python2 and Python.
- use the libraries as built by setuptools, rather than building again
  separately

Work with PkDecryption keys by their private keys

CircleCI Build Support

WebAssembly support