Add methods to obtain pointers to Lua strings directly

[pkhead]

It would be nice if there were methods to obtain direct pointers to Lua strings. These would be an alternative to CheckBuffer and ToBuffer, though I wouldn't mind if OptBuffer didn't get the same treatment. These methods would be unsafe and return a byte*, of course, or probably an IntPtr.

My use case is for passing Lua strings directly into a function loaded from a C library. Currently, I have to use CheckBuffer to obtain the unprocessed character data, then allocate a new byte buffer with an extra byte allocated for the null byte, and then pass it to the C function. This extra processing is a waste of time. Plus, the NativeMethods class is internal, so I couldn't sanely access the function I wanted.

If instead this issue was implemented, it would give me peace of mind.

[viniciusjarina]

Can you send a PR ? Which methods?
You can add new method like IntPtr ToRawString or IntPtr ToRawStringUnsafe