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

Renaming doc files to make the file names more palatable and in preparation for including documentation in sync process