Merge multiprecision from Trunk.

[SVN r81806]
Merge minor fixes from Trunk.

[SVN r81879]
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.

[SVN r82122]
Fix bug in cpp_int division.
Update docs.
Refs #7878.

[SVN r82497]
Merge changes from Trunk.

[SVN r83516]
Merge fix for #8326, plus misc valgrind errors.
Refs #8326.

[SVN r83669]
Merge fix for undefined behaviour/typo.

[SVN r84111]
Merge changes from trunk - support for __float128 and user-defined literals.

[SVN r84295]
Merge doc changes (History update).

[SVN r84298]
Merge doc typo fix.

[SVN r84536]
Merge fixes for from Trunk.
Fixes #8692.
Fixes #8670.
Fixes #8667.

[SVN r84799]
Merge multiprecision changes from Trunk.

[SVN r85681]
Merge multiprecision doc changes.

[SVN r85711]
Update release notes.

[SVN r86350]
End-of-line normalization. Most normalization was taken care of by .gitattributes, but a few files originally committed to svn with incorrect eol tags so need explicit normalization. See .gitattributes man page and extensive list discussion.
Fix PP-logic on test case.
Don't explicitly request gnu++0x mode - it causes conflicts with testers running in c++1y mode.
Merge branch 'develop' of https://github.com/boostorg/multiprecision into develop