Remove references to the GoogleTest mailing list
Fixes #2966

PiperOrigin-RevId: 326065972

The tiny-dnn project has changed the test framework (https://github.com/tiny-dnn/tiny-dnn/commit/d0d35ca2f4e75b3f647787e19ee7f31d0784b398) and removed the googletest usage.

Removing it from the "Who is Using Google Test?" list so as to keep it accurate.

README.dm: Renamed related open source project name: Catch2 and Google Test Explorer -> C++ TestMate

Updated release 1.10.0 link to point to
https://github.com/google/googletest/releases/tag/release-1.10.0 ( that has the
high level release info)

PiperOrigin-RevId: 274147093

Add an announcement about taking a dep on Abseil soon

PiperOrigin-RevId: 272683117

Remove outdated CppCon announcement

PiperOrigin-RevId: 271866311

CppCon announcement

PiperOrigin-RevId: 268950306

Remove outdated summer vacation from readme

PiperOrigin-RevId: 260511450

Update build badge to point to the correct location

point build badge back to proper repo path

Fix build icon location

Closes #587