Fixed oct() builtin error handling - all test cases now pass

[nicklambourne]

Changes

Added correct TypeError reporting for incorrect use of oct() builtin. All incorrect argument types now throw TypeErrors with python-compliant error messages.

Problem

Error handling for unsupported types passed to the builtin oct() method was not python-compliant.

Fixes

Contributes to fixing #47

PR Checklist:

• [x] All new features have been tested
• [x] All new features have been documented
• [x] I have read the CONTRIBUTING.md file
• [x] I will abide by the code of conduct