Airport Codes

First bits of implementation for https://duckduckhack.uservoice.com/forums/5168-ideas-for-duckduckgo-instant-answer-plugins/suggestions/3648798-airport-code-looku

Since this is my first fathead project, I'm not quite sure if I got everything correctly from the readme / the other projects, so please let me know :)

As a result, since it's not very clear to me what the 'trigger' is to use this fathead to answer a query ( I assume the 'abstract' field in the output.txt?! ), this might work for all the three wanted search cases in the plugin idea.

Hope I didn't get everything wrong ...

Cheers,
Phil