Elliptic Curve Signature generation and Verification

Some basic feature implemented for Ellecptic Curve.

1. ecKeyPairGenerator(String curveName): Generates ECKeyPair, shows public key and write private key into a file "privateKey.key".

2. ecSign(KeyPair keyPair, String message): Sign message with its internally generated private key.

3. ecVerify(String sign, ECPublicKey ecPublicKey, String message): Verify a signatue data.

4. genEcPubKey(): Convert a byte array public key into java public key object.