Throw error on parsing multi-octet tag number smaller with tag number 31

[tuxmike]

ITU X.690-0270

8.1.2.2 For tags with a number ranging from zero to 30 (inclusive), the identifier octets shall comprise a single octet
encoded as follows:

8.1.2.4 For tags with a number greater than or equal to 31, the identifier shall comprise a leading octet followed by
one or more subsequent octets.

[lapo-luchini]

Mhh, there are a few places where asn1js is taking a "permissive" approach, others where it is not.
This patch takes the "being precise" approach instead of accepting possibly existing but invalid data… I should probably add a boolean "strict vs permissive" in the parser so that the user can choose.
I'll think about it.