[boost] [multi_index] Doc suggestion.

Subject: [boost] [multi_index] Doc suggestion.
From: Mostafa (mostafa_working_away_at_[hidden])
Date: 2014-11-10 00:19:57

Not being able to mutate elements through non-const iterators is  
surprising enough that I forget about it every time I use  
Boost.MultiIndex. Part of the reason for this is that this information is  
buried under section "multi_index/doc/tutorial/basics.html#seq_indices". I  
suggest that the following paragraph:

"That is, iterators of a sequenced index (of all types of indices,  
actually) point to constant elements. This limitation might come as a  
surprise, but it is imposed by the way multi_index_containers work; if  
elements were allowed to be changed in this manner, we could introduce  
inconsistencies in other ordered indices of the multi_index_container.  
Element modification can nevertheless be done by means of update  
operations."

be moved under "multi_index/doc/tutorial/basics.html#iterator_access" as a  
call-out.