Améliore un poil la clareté de certaines fonctions et la cohérence dans le nommage

• Fix typo
• Rename src to s for functions taking a single argument
• Add {.C} everywhere it was missing
• Change "[...] retourne 0" to "[...] return NULL"(string_chr() returns a char * so NULL must be returned and not 0)
• Rename size to dest_size
• Add an empty line after code blocks to make the text more readable
• Remove trailing spaces