Add custom 'install' command class

CFFIBuild adds ext_modules late in the configuration phase. However,
distutils default 'install' command also parses setup.py and thus misses
that cffi contains several extension modules rather than being pure. As
a consequence, add a CFFIInstall with a proper finalize_options method
and use it.
Add basic DSA backend methods
Remove validation from the backend since it's already done through the API
Add key_size to GC
FIPS 186-2 ECDSA CAVP vectors
FIPS 186-3 ECDSA CAVP vectors
Update docs
Merge pull request #879 from public/ecdsa-vectors

ECDSA vectors from NIST CAVP
Ed25519 test vectors
Update docs
Merge pull request #880 from public/ed25519-vectors

Ed25519 vectors
Merge pull request #872 from saschpe/master-platlib-installation

Add custom 'install' command class
Recommend @lvh's book
add new post-release tasks section to help release managers
Bind a few APIs related to X509_STORE_CTX structures.
Merge pull request #885 from exarkun/X509_STORE_CTX-paraphernalia

Bind a few APIs related to X509_STORE_CTX structures.
some updates to please the spellchecker
Merge pull request #882 from alex/book

Recommend @lvh's book
Merge pull request #884 from reaperhulk/post-release-tasks

add new post-release tasks section
move salt_length from MGF1 to PSS and start deprecation cycle