Add support for context specific types

[huysentruitw]

See #9

[huysentruitw]

From https://docs.ldap.com/ldap-sdk/docs/ldap-wire-protocol-reference/asn1-ber.html, http://luca.ntop.org/Teaching/Appunti/asn1.html and others, I've learned that the current implemented ASN.1 types (Boolean, Integer, Null, etc) are only valid within the universal class range and not for the application or context-specific class, where the tag identifier has a different meaning.

Will probably have to refactor the DerAsnType base class and additionally add the possibility to register class-specific parsers.

cc @qmfrederik

[huysentruitw]

Refactor finished (v3.0)

[cleftheris]

Hi and thanks for your efforts. Is there an example for how todo this?
I have case where I am creating a DerAsnIa5String and serializes perfectly!

var contextSpesificId = new DerAsnIdentifier(DerAsnTagClass.ContextSpecific, DerAsnEncodingType.Primitive, DerAsnKnownTypeTags.Primitive.ObjectIdentifier);
var location = new DerAsnIa5String(contextSpesificId, uri.ToString());
// etc....

But cant seem to get the value out. I tried to hack my way through by doing Encoding.ASCII.GetString(objectIdentifier.Value.Select(x => (byte)x).ToArray()) which gives me almost the string I wanted with missing one character plus two control characters at the begining. Did not like this approach anyway.

What i am trying to figure out is how to tell the default decoder not to parse this into DerAsnObjectIdentifier if it sees the DerAsnTagClass.ContextSpecific but instead parse it into DerAsnIa5String. Can it be done?