Evaluating a rewrite in base R (i.e. drop stringr/stringi dependency)

[Tazinho]

As already thought of in #46 #57 and #89 it might be possible to reduce the dependencies to only base R. Currently the main challenges would be

• stringr offers a local argument, which is usually set to english and allows similar results on different plattforms (indipendently from the locale setting)
• stringi::stri_trans_general etc. which is needed for the transliterations argument doesn't have a similar counterpart in base r.
• however, one would need to slowly translate from stringr to base r, add more conservative test cases and see if further issues pop up