imgui_lua_bindings.pl improvements

[idbrii]

I posted a bunch of PRs to patrickriordan/imgui_lua_bindings.

I see that you have your own improvements here too. Are you interested in merging some of these changes: https://github.com/idbrii/imgui_lua_bindings/tree/all-the-pr

Most changes are in their own branch, but I've given up keeping them tidy and independent unless someone's interested in merging.

Summary:

• combine-shared-logic
  • (DrawList and standard imgui functions
• iterate-enums
  • provide all imgui enums under imgui.constant (e.g., imgui.constant.SetCond.Appearing)
• lua-51
  • define to use lua 5.1 API
• optional-strings
  • support default values for strings
• string-return
  • support returning strings (I think you have this)
• update-to-1.50
  • update to imgui 1.50 (final release is out!)