Generics: add example of any kind

[certik]

Here is one:

https://fortran-lang.discourse.group/t/can-floating-point-literals-be-adapted-by-the-compiler-to-double-precision-variable/2034/102

template log10_tmpl(k)
  integer, constant :: k
  private
  public :: log10
  interface log10
    procedure log10_local
  end interface
contains
  simple elemental function log10_local(x) result(r)
    real(k), intent(in) :: x
    real(k) :: r
    r = log(x) / log(10._k)
  end function
end template

and you use it like:

use kinds_m, only: wp

instantiate log10_tmpl(wp)
real(wp) :: x, y
x = 42._wp
y = log10(x)