Merge multiprecision from Trunk.
Merge minor fixes from Trunk.
Merge bug fixes from Trunk:
Mostly correct typos as per https://svn.boost.org/trac/boost/ticket/7806
Also fix cpp_dec_float docs and add some static asserts to catch misuse.
Fix performance bottleneck in cpp_int's gcd implementation.
Fix bug in cpp_int division.
Update docs.
Refs #7878.
Merge changes from Trunk.
Merge fix for #8326, plus misc valgrind errors.
Refs #8326.
Merge fix for undefined behaviour/typo.
Merge changes from trunk - support for __float128 and user-defined literals.
Merge doc changes (History update).
Merge doc typo fix.
Merge fixes for from Trunk.
Fixes #8692.
Fixes #8670.
Fixes #8667.