updated cmake_minimum_required VERSION to 2.8...4.0

[julian-pfaul]

CMake decided to break backwards compatibility for versions lower than 3.5 since the new version 4.x came out.

After trying to build midifile using CMake 4.0 yields a fatal error:

CMake Error at CMakeLists.txt:1 (cmake_minimum_required):
Compatibility with CMake < 3.5 has been removed from CMake.

Update the VERSION argument value. Or, use the ... syntax
to tell CMake that the project requires at least but has been updated
to work with policies introduced by or earlier.

Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

Since the CMakeLists.txt file is already version 4.0 compatible without any changes necessary, I updated the VERSION parameter of the cmake_minimum_required to "2.8...4.0", to reflect that, and to enable the project to be buildable again using CMake. This should effectily reenable users to build midifile using CMake.

[julian-pfaul]

Additionally I just discovered, that the tools: midi2beep, henonfile, mid2hum, midiexcerpt, and peep2midi were being build dispite the BUILD_MIDILIBRARY_ONLY flag being set. I moved the endif statement of the "if(NOT BUILD_MIDILIBRARY_ONLY)" statement to include these tools.