Initial work to get app_lua.reload rpc command.

Added app_lua.reload rpc command to app_lua module.
Added version var to struct _sr_lua_load in order to know
the version loaded in the child.
Added shared counter sr_lua_script_version in order to notice
the child that it has to reload the script if its version don't
match.
Added function lua_sr_reload_script to increase the shared variable.
Added sr_lua_reload_script to be invoked at app_lua_run
before each call.
Removed silly var. Follow the code style.
Add documentation