castValueBidirIterator and castValueForwardIterator are two class that
take control of an iterator 'it'. Both change information type pointed by
'it' by use of static cast. So compare to 'it' only operator * is
changed. The type used during casting is provided as a template
parameter to those class.

These classes aim to replace entitytovertexiteratorconvertor class of FM
library which was used as a start for construction of this new family.
Compare to this original version, iterator category coherence is more
strongly achieved between 'it' and its warper. To simplify user task the
function makeCastValueIterator provide a simple way to create
castValueBidirIterator or castValueForwardIterator depending on 'it'
iterator category type.

As now cast type is a template parameter the user have more choice.
The reverse operation (mVertex* to mEntity*) have been for example
tested successfully in some appli. And in the same appli use of those
class in replacement of entitytovertexiteratorconvertor was ok.

TODO
replace entitytovertexiteratorconvertor and certainely also
citerobjecttovertexiteratorconvertor
Add other category type and maybe do some rearrangement to minimize code
duplication.