Huge changes to bidimap and added callbacks to it

Callbacks lost their 'on_' prefix
Bidimap was simply not working properly. Many of its functions have been reworked:
- _update_key_by_val is now _update_key
- _update_val_by_key is now _update_val
- Removed _update_key and _update_val because they just weren't what a bidimap really is about

TODO

@@ -31,7 +31,6 @@ TODO
 [ ] Use binary search to find optimum hashtable prime size inside impl_calculate_size
 [ ] Optimize certain loops that use iterators but can simply use a normal loop
 [ ] Replace IntervalHeap node by a simple buffer of two pointers (V (*buffer)[2])
-[ ] Merge bidirectional map key_buffer and val_buffer to a single buffer and make key_dist and val_dist into dist[2]
 
 #!! Done -------------------------------------------------------------------------------------------
 
@@ -64,3 +63,4 @@ TODO
 [X] Add Function Tables that contains data type functions
     (compare, copy, display, free, hash, priority)
 [X] Add error codes that can be accessed from the collection's struct
+[X] Merge bidirectional map key_buffer and val_buffer to a single buffer and make key_dist and val_dist into dist[2]