Enough compatibility work to make figlet build and run!

I ran out of steam writing library routines and imported two
BSD-licensed libc routines: sscanf() and getopt().

I will most likely rewrite them sooner or later. For now
I just wanted to see figlet running.

LibC/stdlib.h

@@ -9,7 +9,8 @@ void* malloc(size_t);
 void free(void*);
 void* calloc(size_t nmemb, size_t);
 void* realloc(void *ptr, size_t);
-
+char* getenv(const char* name);
+int atoi(const char*);
 
 void exit(int status);
 void abort();