Use Array.prototype.slice

Instead of a loop with popping. That's silly.
Add BOOLEAN types

Not used for Kerberos, but it's in the X.690 examples. So are the random
string types, but I'll change them to GeneralString.
Fix OID ASN.1 implementation

Ooops. Might be helpful to actually look at the spec.
Add method to make implicitlyTagged type
Basic ASN.1 tests

Need a more complex test though.