RomanNumerals fixed

[hhaensel]

I've merged the open issues in RomanNumerals.jl so that PDFIO is now compatible with Julia 1.7

• https://github.com/anthonyclays/RomanNumerals.jl/issues/12
• https://github.com/anthonyclays/RomanNumerals.jl/issues/13
• https://github.com/anthonyclays/RomanNumerals.jl/pull/11
• https://github.com/anthonyclays/RomanNumerals.jl/pull/15
• https://github.com/anthonyclays/RomanNumerals.jl/pull/16
• https://github.com/anthonyclays/RomanNumerals.jl/pull/17