[flyweight] Review summary

Hi to all,

I've just written a summary of the flyweight review that tries to point 
out the main requests, questions and comments from reviewers and 
Joaquin's replies to those. If someone thinks I've missed some important 
point, please let me know.

Joaquín is already correcting the pointed issues and thinking about 
alternatives on the keyed_flyweight issue. I hope we can definitely 
solve them satisfactorily in a short period of time. Here we go:

--------------------------
      Beginning of summary
--------------------------

-------------------------
*Tim Blechmann’s review:*
-------------------------

Design: Good. Suggests using read-write locks to improve concurrency 
since most operations will be searches.

Implementation: fine

Documentation: good

Usefulness: quite useful to reduce memory footprint.

Try to use the library: no