Use error class for error messages

(Makes it easier for parser functions like #iferror to detect errors)
Merge pull request #8 from lethosor/asvae-master

Use error class for error messages
Add MW fix and multiple files support to loadFile

* MW ! fix autodetects "Masterwork" folder. In case of copypasted raws,
"FIX!" as option is required.
* blocked graphic tileset support for background color, big squares
after saving page
Forgot echo.
Optimisation, arrayfication, non fuctional version
Merge branch 'asvae-master' into asvae-readme