Preparation for including docs in round-trip with OSS, Manual merge, review and merge docs internal-OSS

Internal change

PiperOrigin-RevId: 258587862

PiperOrigin-RevId: 258465918

gmock-spec-builders.h uses std::function (in MockFunction) but did
not include <functional> to provide it. Apparently, it worked since
the header must have been included by something else but better be
safe than sorry.

Fix documentation links

PiperOrigin-RevId: 258389329

[Fuchsia] Update exception APIs used by death test.

Migrates to the new channel-based exception APIs as the
port APIs are deprecated and will be removed.

PiperOrigin-RevId: 258175830

Update a broken link in a comment.

PiperOrigin-RevId: 257493975

Fix a broken link

Travis CI: The sudo: tag is now deprecated in Travis CI

ee3aa831 added a broken link
which results in 404. The broken part is reference to a
nonexistent file "CheatSheet.md" instead of "cheet_sheet.md".

Add missing references to documentation

This line directly contradicts the warning that google mock spits out on unused mock calls:
```
NOTE: You can safely ignore the above warning unless this call should not happen.  Do not suppress it by blindly adding an EXPECT_CALL() if you don't mean to enforce the call.  See https://github.com/google/googletest/blob/master/googlemock/docs/CookBook.md#knowing-when-to-expect for details.
```
One or the other should be changed, and I believe the advice in this file is incorrect.

Remove google internal links from documentation on github