First attempt at issue.
Tidy up mangled comments
Add scalbn and logb functions, plus float->rational generic conversion (base 2 only at present).
Add scalbn, ilogb, logb and tests and docs.
Implement exact base-10 floating point to rational conversion.
Tentative implementation of exactly-rounded rational to float conversions.
Update and enhance tests.
Commit test file and improve tests some more.  Fix some bugs too!
Fix rounding bug in cpp_bin_float - in the case that the remainder is zero, we may still have a tie if the extra bit in the quotient is one.
Fix warnings and compiler errors, plus rounding error in generic_interconvert.hpp.
Add comments about rounding to gmp.hpp.
Update tests to check mpq_rational.
Enable correct rounding for mpq_rational -> floating point conversions.
Merge branch 'develop' into Issue_10085
Update docs.
Merge branch 'Issue_10085' into develop

Resolved conflicts:
	doc/html/index.html
	doc/multiprecision.qbk

Remove already done items from TODO list.