lang: Fix typo

lang: Check stack depth before accessing elements ...

I tested this code by hand, make sure to do the same if changing.

lang: Remove useless object cleanup checks ...

Once again we assume that we've gotten here correctly based on class data.

lang: Simplify number functions

lang: Check values since we're kind of testing anyway

lang: Add depth checks to compiler calls

lang: Add depth check bytecode

lang: Remove object_class forward declaration

lang: Set extra variables to NULL after dropping

lang: Always place VmState first in function calls

lang: Remove arg_count and rely on stack depth instead

lang: Hide VmState internals

lang: Add opaque types for Object and VmState

lang: Use stack offsets instead of pointers

lang: Handle vm_state creation in vm

lang: Switch to callee cleanup of non-return arguments ...

This simplifies calling things and will allow proper tail calls.

lang: Create vm state once in main

lang: Add back reference counting ...

The basic idea here is that we transfer ownership to and form the stack,
and clean up references that way.

lang: Clarify what skipping over ASCII and unknown OPs means

vm: Add stack pushing and popping

lang: Use vm_stack_get and set for OP_GET and OP_SET

lang: Rename vm.stack to vm.stack_next

lang: Add stack bases to vm

lang: Remove checks for obj->class_data ...

I have no idea how these could even trigger.

lang: Drop reference counting, embrace leaking ...

I will add proper garbage collection later

lang: Wrap stack functions

number: Don't check if return is NULL ...

This doesn't really matter since we will overwrite it

lang: Replace args with a vm_state stack ...

This doesn't have any functional changes at the moment but will
aid in adding proper stack support in the future.

lang: Fix Return register being wrong

lang: Check for undefined variables