Add documentation to transform_inclusive_scan and transform_exclusive_scan

[jgopel]

Hi @glenfe - Thanks for the feedback - I hadn't yet noticed the "Not-yet documented" section of that quickbook. Please let me know if there are any other changes I can make to help this land.

[glenfe]

Thanks @jgopel . This looks better now. To be complete, it should probably also add sections for the now documented functions in the CXX17_inner_algorithms documentation section.

i.e. In this block: https://github.com/boostorg/algorithm/blob/develop/doc/algorithm.qbk#L100-L109 we need something like:

[section:transform_inclusive_scan transform_inclusive_scan]
[*[^[link boost.algorithm.transform_inclusive_scan    transform_inclusive_scan]    ] ]
Transforms elements from the input range with an operation and then combines
those transformed elements with an operation such that the n-1th element and
the nth element are combined. Inclusivity means that the nth element is included
in the nth combination.
[endsect:transform_inclusive_scan]

And a similar section for transform_exclusive_scan

[jgopel]

Done 🙂 Based on the existing entries in the quickbook, I kept the description a little shorter there and left the longer description for the linked page. If you'd prefer a different approach, just say the word!