docs: Fix a few typos

There are small typos in:
- example/ex-algo03.c
- m-algo.h
- m-core.h
- m-dict.h
- m-string.h

Fixes:
- Should read `occurrence` rather than `occurence`.
- Should read `fulfilled` rather than `fullfilled`.
- Should read `dictionaries` rather than `dictionnaries`.
- Should read `environment` rather than `environement`.
- Should read `unordered` rather than `undordered`.

example/ex-algo03.c

@@ -3,7 +3,7 @@
 #include "m-algo.h"
 #include "m-string.h"
 
-/* Define a dictionnary (or hash_map or undordered_map)
+/* Define a dictionnary (or hash_map or unordered_map)
  * from a string_t to int */
 DICT_DEF2(dict, string_t, int)
 /* Register the oplist of this dictionnary globally */