Change table access to optionally not create tables if they do not exist

[dcat52]

I would like to propose the following implementation changes to BuzzTableOpen and BuzzTableOpenNested.

• Addition of an optional parameter make_if_not_exist to specify whether the table should be created if it does not already exist and have it default to true for backwards compatibility.
• Change return type from void to bool to notify the user if the table open was successful.

Example Usage:

bool success;

success = BuzzTableOpen(t_vm, "tbl", false);
if(!success)
    return;
success = BuzzTableOpenNested(t_vm, "A", false);
if(!success)
    return;