Minor coding style fixes

This makes a number of changes:
  * Remove the dependency on marshal by using string.dump and loadstring.
  * Use lua_tolstring rather than having Lua functions pass string lengths to C++.
  * Move lua_api/l_async_events.* to cpp_api/s_async.*, where it belongs.
  * Make AsyncWorkerThread a child of ScriptApiBase, this removes some duplicate functionality.
  * Don't wait for async threads to shut down.  (Is this safe?  Might result in corruption if the thread is writing to a file.)
  * Pop more unused items from the stack
  * Code style fixes
  * Other misc changes

Add support for (configurable) multiline hotbar
Improved screensize handling
Add userdefined gui scale by BlockMen

This reverts commits a2003b0d and 54ffe2e5.

These weren't correct.  Add a black magic warning instead.

Thats updated #795

Add log entry for peer timeout

add c++11 atomic support (optional)