jex_vm: Objects

Changelog

1. added objects: NEW_INSTANCE, GET_FIELD and SET_FIELD instructions

jex_vm

jex_vm was extracted from extendable_vm into a separate repo.

Changelog(all previous versions combined):

• added TO_STRING, READ_LINE and PARSE_INT instructions
• Function calls and returns
• Better error messages and error types
• Better errors for code parsing
• Better errors for operator instructions
• VM prints stack trace when errors are raised
• Better unit tests
• Exceptions + stack trace