Add example / error in documentation

[hiker]

It would be great to have an executable example, so it makes it easier to see what is happening, and what needs to be done to a code. I am aware that they are tests, but see #149.

I also believe there is a mistake in the documentation. The file documentation./Sphinx/user_guide/api.rst contains:

./Sphinx/user_guide/api.rst:   integer (kind=pik) :: vernier_handle

I don't see pik defined anywhere:

~/work/vernier$ grep -ir pik 
grep: .git/objects/pack/pack-cdf4447b72218c052ac5474be4c5f4d464fc3610.pack: binary file matches
documentation/Sphinx/user_guide/api.rst:   integer (kind=pik) :: vernier_handle

Is that supposed to be vik?

src/f/vernier_mod.F90:  integer, public, parameter :: vik = c_long

?