crypto: add ECDH test vectors for more curves

Vectors have been taken from NIST's CRYPTOGRAPHIC ALGORITHM VALIDATION
PROGRAM (CAVP) (http://csrc.nist.gov/groups/STM/cavp/)
crypto: move elitic curve definitions from OpenSSL built-ins to Erlang

Decouple eliptic curve definition from OpenSSL and define them in
Erlang.
crypto: add brainpool (RFC 5639) curves

RFC-5649, Section 1, documents the advantages that these curves
might have over others (ANSI, SEC1/2)
crypto: document ec_curves/0 and ec_curve/1
public_key: add brainpool elliptic curves (RFC-5639)
ssl: add brainpool elliptic curves to TLS (RFC-7027)