Use this function to append a string at the end of another. This function is advanced considering the usual C strcat command: it does bound checking so you don't have to do any control before appending.
Destination string. This string MUST be an AFC string created using afc_string_new()
Source string. This string can be anything, a static string, an AFC string , a memory area...
Here you can specify how many chars to copy. Pass the value ALL to copy the whole string.