Add possibility to program SNMP response value

[delimitry]

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

• [x] BOOLEAN
• [x] INTEGER
• [x] BIT STRING
• [x] OCTET STRING
• [x] NULL
• [x] OBJECT IDENTIFIER
• [x] REAL
• [x] DOUBLE
• [x] IP_ADDRESS
• [x] TIMETICKS
• [x] GAUGE32
• [x] COUNTER32
• [x] 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