Add support for more subtitle filetypes

[aidancrowther]

Currently, only SRT subtitles are supported, we would like to expand this to more filetypes such as SSV and ASS. To do this you will need to check the file extension and then reimplement the subtitle loader system to load in the same style with these new formats.

This code can be found in loadSubs in the main.c file, by loading the data into the subtitle array in the format described within this function subtitle rendering should work.