bump version to 1.5.0.dev to align with core
resolves #16 fix broken ebook-format-epub3 attribute
bump Asciidoctor dependency to ~> 1.5.0
add front-cover-image attribute, leave commented
only select euro symbol from extended currencies

- only select euro symbol from extended currencies in font script
- add note about cmap format 14 table error
update WORKLOG