Update composer dependencies.
Use setLevel in pssht.xml.

This allows for slightly less verbose logs (we avoid level 5 logs).
Add support for chacha20-poly1305.

See the following references for details:
- https://tools.ietf.org/html/draft-nir-cfrg-chacha20-poly1305-06
- http://cr.yp.to/mac/poly1305-20050329.pdf
- http://cr.yp.to/chacha/chacha-20080128.pdf

Fixes #14.