Add callee function listing feature

[nonetype]

• Adds callee listing feature
• param: the function address to get callees
• return: list of callee informations (address, name and type - internal or external)

>>> get_callee("0x417C7E")

[
  {'address': '0x415cc3', 'name': 'sub_415CC3', 'type': 'internal'}, # internal - the code exists in same binary
  {'address': '0x415da9', 'name': 'sub_415DA9', 'type': 'internal'}, 
  {'address': '0x4181cd', 'name': 'sub_4181CD', 'type': 'internal'}, 
  {'address': '0x417e06', 'name': 'sub_417E06', 'type': 'internal'}, 
  {'address': '0x415e1c', 'name': 'sub_415E1C', 'type': 'internal'}, 
  {'address': '0x44d264', 'name': 'exit', 'type': 'external'}, # external - imported from other libs
  {'address': '0x417b37', 'name': 'sub_417B37', 'type': 'internal'}
]

[mrexodia]

Apologies for the delay and thanks!