Test Vector changes

Changed names of existing vectors to be more instructive about what the
key contains, and adapted tests to compensate, which pass. Added public
keys for all encryption types and two new private keys for PEM
serialization, documented in the README.txt in the same folder
Part 1 of rebase, with corrections for pep8
Initial cleanup
Reorder
flake8
Try to simplify
Remove duplicate class and fix name
Added some docs
Added a unit test
A test for DSA
another test
Tests for multi backend
Remove passwords for public keys
document the interface
Finalised merge of files
Merge branch 'public_key_pem' of https://github.com/michael-hart/cryptography into public_key_pem

Conflicts:
	cryptography/hazmat/backends/interfaces.py
	cryptography/hazmat/primitives/serialization.py
	docs/hazmat/backends/interfaces.rst
	docs/hazmat/primitives/asymmetric/serialization.rst
	tests/hazmat/backends/test_multibackend.py
	tests/hazmat/primitives/test_serialization.py
	vectors/cryptography_vectors/asymmetric/PEM_Serialization/README.txt