convert: merged file writing procedures

also, a lot of random improvements...
convert: better status message when generating texture atlas
convert: fixed swapping subtexture width and heigh assignments
convert: put image files in the write directory
convert: added invokation argument for selecting dat file sections
convert: moved data formatting code to separate file
convert: create metadata list of extracted sounds
convert: implemented enum values for csv columns
convert: include string header, updated filename for soundlist header
Merge branch 'convertdat' into audio
audio: add resource loading via sound_file vector