C++11 doc cleanup:
C++11 doc cleanup:

Changes with a visible effect:

* Always comma-separate multiple items
* Generally avoid <br>s except where listing code
* Use the phrase "Google Style Guide", not "Google style guide", "C++ style guide", "Google Style Guide on XXX", etc.
* declval item was in the wrong section, written poorly, and had broken links
* Remove notes about MSVC2013 caveats
* Fix formatting of code (use correct number of spaces, etc.)
* Remove notes about FINAL and OVERRIDE macros, they're dead
* Slight clarification to nullptr instructions to make it clear that replacing NULL in existing code is OK
* Remove note forbidding general use of std::tuple since we explicitly allow general use of std::tuple
* Change comments like "Reevaluate once MSVS2015 is available" to "Reevaluate now that MSVS2015 is available"
* Add missing links to style guide for various banned items
* Various other tiny wording fixes/clarifications

Changes with no visible effect:

* One space after a period
* No line length limit (makes it easier to find an item to edit when scrolling through doc, matches how half of doc was already working, wrapping was very inconsistent otherwise)
* Collapse together sequential <code> blocks with no intervening text

BUG=none
TEST=none

Review URL: https://codereview.chromium.org/1892473003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#387445}

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