Improve caching on get_theme_mods function

[spacedmonkey]

Currently whenever the get_theme_mods function is called, it calls the also the get_options function twice. This means that whenever the get_theme_mod / set_theme_mod / remove_theme_mod , also makes a call to options table. This value is not cached in memory, so whenever get_theme_mod is called it will get the values from the db / object cache.

To improve performance, after the first time the function is called, theme mods should be stored as a global / static variable.