Add possibility to program SNMP response value

[delimitry]

Support config file for programming the responses.
May be, it is required to support OID wildcards 🤔
For example:

{
    "*": lambda oid: str(oid),  # to return OID string value as a response to every request
}

Or:

{
   "OID1": "string",
   "OID2": 12345,
   "OID3": Timeticks(123456000),
   "OID3": random.randint(1, 10),
}

This requires ability to write values for ASN.1 types.

• BOOLEAN
• INTEGER
• BIT STRING
• OCTET STRING
• NULL
• OBJECT IDENTIFIER
• REAL
• DOUBLE
• IP_ADDRESS
• TIMETICKS
• GAUGE32
• COUNTER32
• COUNTER64
• ENUMERATED
• CHARACTER STRING

[delimitry]

Add new ASN.1 types in PR #8.

[delimitry]

Add config file support & new ASN.1BIT STRING type in PR #9