postprocess string/regex behaviour about snakecase HOT 1 CLOSED

the problem ist introduced within the block

## protect (the protector is needed to clean up the separator around the 
  # protected field)
  postprocess_protector <- if(is.null(postprocess)){
    "_"
  } else {postprocess}
  
  if(!is.null(protect)){
    protect <- stringr::str_c("([", protect, "])")
    infront <- stringr::str_c(postprocess_protector , "+", protect)
    behind <- stringr::str_c(protect, postprocess_protector, "+")
    string <- stringr::str_replace_all(string, infront, "\\1") %>% 
      stringr::str_replace_all(behind, "\\1")
  }

It should be solved by a more logical rewrite of to_any_case in the following way:

1. preprocess & parsing (must come first)
2. protect (protected symbols become cleaned, when we apply this new order, at this step only "_" must be cleaned)
3. replace special characters (must come before preprocess; capital letters like Ä must be replaced via Ae)
4. cases (but still with underscores around)
5. (a & b) postprocess and cases:
   • split every string and paste it together with the string supplied to postprocess
6. prefix and postfix

from snakecase.