add missing implicit none, set compiler flags to force implicit none

[scivision]

also set minimum CMake version to 3.14 per prior discussion and add example check requiring CMake 3.14: real128

[certik]

I've never used -fimplicit-none. Should that be recommended to be used by default for all modern Fortran projects?

[scivision]

yes -fimplicit-none was available at least back to Gfortran 4.1 (didn't try looking further back) and I don't think there are any drawbacks.

[certik]

@scivision cool. This is relevant to: j3-fortran/fortran_proposals#90.

[certik]

Thanks for the improvements!

[zbeekman]

Thanks all!