Validating of public key curve point.
Tests for public key validity check.
Removed unnessary point copy.
Merge pull request #9 from hiviah/ecdsa_pubkey_validation

ECDSA public key validation
make pubkey validation optional, extract options to separate header
normalize y^2 in pubkey validation
fix last commit
rename BN_PRINT define to USE_BN_PRINT
use more warnings from trezor-mcu