Lenient parsing of default values

[joyantaDebnath]

Based on X.690 DER restrictions (section 11.5), when encoding a set or sequence, any field that is equal to its default value shall not be included in the encoding. Nevertheless, ZLint’s parser does not adhere to this requirement and reports errors for specific fields that have default values, such as the CA flag of the Basic Constraint extension, the critical flag of extensions, and the Version.

[CBonnell]

I think this is a duplicate of #639.