Follow transliteration of non-ascii characters as well as reasonably possible

created by @dimus at https://gitlab.com/gogna/gnparser/-/issues/48

ICN 60.6. Diacritical signs are not used in scientific names. When names (either new or old) are drawn from words in which such signs appear, the signs are to be suppressed with the necessary transcription of the letters so modified; for example ä, ö, ü become, respectively, ae, oe, ue; é, è, ê become e; ñ becomes n; ø becomes oe; å becomes ao. The diaeresis, indicating that a vowel is to be pronounced separately from the preceding vowel (as in Cephaëlis, Isoëtes), is a phonetic device that is not considered to alter the spelling; as such, its use is optional. The ligatures -æ- and -œ-, indicating that the letters are pronounced together, are to be replaced by the separate letters -ae- and -oe-.

ICZN 32.5.2.1. In the case of a diacritic or other mark, the mark concerned is deleted, except that in a name published before 1985 and based upon a German word, the umlaut sign is deleted from a vowel and the letter "e" is to be inserted after that vowel (if there is any doubt that the name is based upon a German word, it is to be so treated).

We need to decide on a 'less harmful' approach here.

gnames / gnparser

Follow transliteration of non-ascii characters as well as reasonably possible #48