Handling of abbreviations and other characters

[jens-totemic]

When converting e.g. this sentence:
"TTS comes with pretrained models, tools for measuring dataset quality and already used in 20+ languages for products and research projects."

In that sentence the abbreviation "TTS" is not correctly converted to letter by letter (instead it's converted to an incorrect word) and the "+" in 20+ is also omitted.

I originally filed this here: espnet/espnet#2990 (comment) . Is this handling of abbreviations and other special characters something that could be added to g2p?