cmake: Add fatal-warnings option

This makes compiler warnings become errors.
cmake: Remove unneeded FindDoxygen include
cmake: Remove known warnings for gtest build
Merge pull request #1394 from rleigh-dundee/cmake-fixes3

CMake: Fixes for fatal warnings and doxygen
Update auto-generated documentation

Repository: openmicroscopy/bioformats
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Generated by BIOFORMATS-5.1-latest-docs-autogen#183 (http://ci.openmicroscopy.org/job/BIOFORMATS-5.1-latest-docs-autogen/183/)