CMake fix

Minor Cmake fixes:

• min. required cmake version: 3.12 (was 3.5)
  • CMAKE_PROJECT_HOMEPAGE_URL attribute was added there
  • add_compile_definitions was also added with there (link)
• remove escaped qoutes from add_compile_definitions as an attempt to fix #160 (closed) (guess: cygwin could have problems with escaping characters)

Fixes #160 (closed)