add Extended Key usage extension
make sure the key usage flag list is sorted before testing
add tests for Extended Key Usage.
bump version to 1.4.7
requires 1.4.7 as minimum version in validation.
make the key usage check conditional on the existence of the extension.

if the KeyUsage extension is not present then the certificate key usage
is not restricted and thus everything goes.
add a simple way to check the ExtendedKeyUsage too if needed.
bump version to 1.4.7
show ExtendedKeyUsage too in the list if present.
bump version to 1.4.2