require crypto-number 0.2.2
use safe/fast variants of expmod where needed
Add ECC arithmetic primitives

This includes point addition, doubling and multiplication.
Add ECDSA signature generation
Add ECDSA signing and verification
Add ECDSA QuickCheck tests

This includes:
 - Arbitrary message with fixed prime curve.
 - Arbitrary message with fixed binary curve.
 - Fixed message with arbitrary curve.
Add benchmarks for secp160r1 and sect163k1
Add KAT tests for ECDSA
Update documentation