Cached files so they are only loaded once
Cached files so they are only loaded once

`files` is an expensive method and is called a number of times. Added caching of the files and reload them in certain conditions

jwhitcraft/sinatra-assetpack,flywithmemsl/sinatra-assetpack,jwhitcraft/sinatra-assetpack,rstacruz/sinatra-assetpack,flywithmemsl/sinatra-assetpack,rstacruz/sinatra-assetpack,flywithmemsl/sinatra-assetpack,rstacruz/sinatra-assetpack,jwhitcraft/sinatra-assetpack