Add an option to export aseprite file into several .png files

[dacap]

This could be done from the command line, as another parameter like --sheet

The export operation could be by frames, by layers, or both (e.g. export each cel into a separate png file)

[ghost]

+1

[mtmbTomSmith]

if you save your project as a .png, if your file has multiple frames it will export the series as
projectName0, projectName1, projectName#etc. It doesn't do the individual layers though

[dacap]

A new --save-as parameter was added. Also now we can split layers with a --split-layers parameter, but it only works for sprite sheets at the moment. Ref: ce962f4