Great changes

[guidanoli]

It's basically a diff between my fork and the original repo

Legend: +additions -removals *changes
+ stack context handler (locks runtime, checks extra slots in stack and restores stack top)
+ better panic function (prints the Python stack before Lua aborts the program)
+ proper error handling between Lua and Python
+ wraps Python exceptions + tracebacks in a _PyException object
+ converts Lua traceback to Python traceback
+ python.exec (lupa.LuaRuntime.execute counterpart)
+ 'register_exec' option, defaults to True
+ python.PYTHON_VERSION (lupa.LUA_VERSION counterpart)
+ python.pack (Lua values -> Python tuple, like table.pack)
+ python.unpack (Python tuple -> Lua values, like table.unpack)
+ python.is_object (for checking if Lua value is a wrapped Python object)
+ python.is_error (for checking if Lua value is a wrapped _PyException object)
+ adds assertions for catching Lua C API misuses (e.g. indexing non-tabular value)
+ caches Lua objects
+ add tests
+ add '--gdb-debug' option for compiling with gdb debug information
* made names in the registry more descriptive to avoid conflicts
* simplified library registration
* simplified _LuaObject getter/setter/delete methods
* use lua_pushglobaltable for Lua 5.2+
* made lock_runtime return 0 on error, instead of raising error
* simplified _LuaThread.__bool__ and resume_lua_thread
* overflow handler defaults to returning wrapped Python integer to Lua
* py_to_lua raises an error instead of returning 0
* py_to_lua_custom raises an error instead of returning 0
* calling Lua functions from Python doesn't need to set stack top to 0
* unpack_multiple_lua_results (now py_tuple_from_lua) works with top 'nargs' elements
* make python.args be usable only in the last position to respect Lua semantics
- _LuaCoroutineFunction (messes up Lua caching)

[guidanoli]

I know this is a lot, but could you review this PR, @scoder?

[scoder]

Sorry, no. I don't have the time to review that amount of changes. Even worse, they're literally mixed together into one big commit, which makes it impossible to know why a specific piece of code was changed.

If you can cut the changes down into separate feature/fix PRs, I can try to review those.

As it stands, I cannot possibly review this, let alone merge it.