move googlemock files into googlemock/ subdir

googlemock/CHANGES

googlemock/CMakeLists.txt

googlemock/CONTRIBUTORS

googlemock/LICENSE

googlemock/Makefile.am

googlemock/README.md

googlemock/build-aux/.keep

googlemock/configure.ac

googlemock/docs/CheatSheet.md

googlemock/docs/CookBook.md

googlemock/docs/DesignDoc.md

googlemock/docs/DevGuide.md

googlemock/docs/Documentation.md

googlemock/docs/ForDummies.md

googlemock/docs/FrequentlyAskedQuestions.md

googlemock/docs/KnownIssues.md

googlemock/docs/ProjectHome.md

googlemock/docs/v1_5/CheatSheet.md

googlemock/docs/v1_5/CookBook.md

googlemock/docs/v1_5/Documentation.md