Merge branch 'adjust-compiler-warnings' into 'master'

cmake compiler flag cleanup, enable many clang warnings and fix them

See merge request !63
9 jobs for master in 3 minutes and 58 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #75806
VS2015
VS2015-32-bit

00:01:11

passed #75805
VS2015
VS2015-64-bit

00:01:23

passed #75804
VS2017
VS2017-32-bit

00:01:16

passed #75803
VS2015
VS2017-64-bit

00:01:26

passed #75800
Linux
clang-c++11

00:03:58

passed #75802
Linux
cppcheck

00:00:23

passed #75807
Linux
doc

00:00:20

passed #75799
Linux
gcc-c++11

00:03:54

passed #75801
Apple
macos-c++11

00:01:38