Read theme file using UTF-8 encoding

[mojavelinux]

Asciidoctor PDF should be able to read a theme file containing characters outside the ASCII range even when the system is not configured to use UTF-8 encoding. To support this scenario, the theme file should be force encoded (i.e., coerced) to UTF-8 encoding.

[mojavelinux]

To test, use a non-ASCII character in the running content (e.g., Romé), then set the LANG environment variable to C when invoking asciidoctor-pdf:

LANG=C bundle exec ./bin/asciidoctor-pdf sample.adoc

[mojavelinux]

Actually, since Asciidoctor PDF requires at least Ruby 1.9.3, we can simply set the encoding when reading the file.

IO.read filename, encoding: ::Encoding::UTF_8