This commit fixes a bug where AsciiDoc would drop any line containing a
'{foo}' because it interpreted it as an undefined attribute reference:
> Simple attribute references take the form {<name>}. If the attribute name
> is defined its text value is substituted otherwise the line containing the
> reference is dropped from the output.
See: https://www.methods.co.nz/asciidoc/chunked/ch30.html
We fix this by simply replacing all occurrences of '{' and '}' with
their escaped forms: '{' and '}'.
Fixes#1101