Merge pull request #10 from jdnavarro/master

Changes needed for ECDSA
add haddock comment for keypair
bump version to 0.4.1
add ASN1 OID for CurveName
add some pointers in description of implementations.
add some instance for CurveName.
move PublicPoint and PrivateNumber to ECC.
bump version to 0.4.2
correct some OID.
bump version to 0.4.2.1
support bad ASN1 implementation negative modulus

openssl has the same behavior.
bump version to 0.4.2.2