Update minimum cmake version from 2.8.12 -> 3.5

[nredick]

CMake 2.8 has been deprecated, resulting in failing build. Update to 3.5

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

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

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


-- Configuring incomplete, errors occurred!

[MFraters]

Thanks for making this pull request!

I do have to note that there are a lot of unrelated lines changes in this pull request. Normally the spelling fixes for example would go into a separate pull request. You are also changing the spaces of many lines. Normally I would ask you to revert this, but looking at them they seem to make sense so I will let it pass for this time. I suspect they are changed automatically by your editor, so I would like to ask you to turn that off in the future. The reason for this is that editors may have slightly different conventions, which may lead to the same unrelated lines being changed back and forth between pull request. What probably should happen is that the indent script should be extended to these files as well.

Anyway, thanks for the fixes!