Inaccuracies on intro page for range adaptors

[Nathan Ridge]

The "Introduction and Motivation" page for Range Adaptors has a number of issues:

1. The example where a use of boost::count_if is replaced by boost::count + the filtered adaptor is conceptually wrong (there is no reasonable value to pass as the second argument to boost::count to get the desired behaviour). In the example, a bogus argument called 'out' is passed.

2. More generally, the claim that "[in light of range adaptors] no algorithm with the _if suffix is needed" is misleading. See my analysis in this post for details: ​http://boost.2283326.n4.nabble.com/range-count-vs-count-if-tp4374377p4388398.html

This section of the documentation needs to be cleaned up a bit, and it perhaps needs to make less bold claims :)

[Neil Groves]

Corrected in the .qbk on the develop branch.

[Neil Groves]

merged .qbk to master - html will be removed from git and put into build before 1.56