Instructions for further updates:
- download new version of googletest
- use ``googletest/scripts/fuse_gtest_files.py`` to obtain only ``gtest.h`` and ``gtest-all.cc``
- (optional) manually apply clang-format (on a beefy computer) to ``gtest.h``
- suppress warnings in gtest.h by inserting (compare old version of gtest.h)
```c++
 #if defined(__clang__)
 #  pragma clang system_header
 #elif defined(__GNUC__)
 #  pragma GCC system_header
 #endif
```
- insert ( compare old version of ``gtest-all.cxx``)
```c++
```
at the beginning of ``gtest-all.cxx`` and
```c++
```
at the end.

closes #56