- Don't use negative indicies to read arguments of Lua functions.
- On error, return nil, "error string".
- Use ssize_t for return values from bozo_read() and bozo_write().
- Prefer lstring especially when if saves you from appending NUL and
doing len + 1 which can potentially wraparound.
- Don't mix C allocations with Lua functions marked with "m" in the Lua
manual. Those functions may throw (longjump) and leak data allocated
by C function. In one case, I use luaL_Buffer, in the other case,
I rearranged calls a bit.
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