Find Fortran subroutines defined in interface blocks

[billsacks]

This finds generic procedures defined like this:

  interface endrun
     module procedure endrun_vanilla
     module procedure endrun_globalindex
  end interface

(where you're looking for the definition of 'endrun').

Since there is no instance of subroutine endrun (...) (only subroutine endrun_vanilla (...) and subroutine endrun_globalindex (...)), this change is needed in order to find the place where endrun is defined.

[billsacks]

Thanks a lot for this very useful package!

Some caveats:

1. I wasn't able to get cask to work, so wasn't able to run the tests on this change

2. I have only been using this package for a day, and this change for a few minutes, so it's possible that this change does the wrong thing in some situations. If you prefer to wait to merge this until I have more experience with the change, that's fine.

[coveralls]

Coverage remained the same at 97.063% when pulling 39f9b28 on billsacks:fortran_interface into 9e79b74 on jacktasia:master.

[jacktasia]

Thanks for the PR and kind words!