handle tab characters tab characters have their width depending on the column they're in, since they extend to the next multiple of 8. (citation needed?) So, keep track of the column when considering the length (in columns) of the text, so that we can render them properly. In the future we might want to turn them into spaces (either at read or render time) just to stay on the safe side in case not all terminals/ncurses implementations use 8 columns.

mark utf8_chwidth as static

retire utf8_encode too, it's no longer used

remove now unused fuctions from utf8.c

use a byte offset to track the point in the line Instead of using a code-point offset, use a raw byte offset and navigate backward and forward by means of graphemes. This gives a correct "visual" backward/forward navigation through characters.

typos; courtesy of codespell

some headers cleanup try to not include headers from headers, and remove some redundant include. This helps in modularizing the codebase and also helps during incremental compilations.

move all the sources back in the root directory subdir is just messier for no good reason