Make character variables in Fortran have arbitrary length

[edoddridge]

As identified in #121, the length of character variables used to store the input filenames can be an issue if the names become quite long.

A quick fix of increasing the max length from 30 to 60 characters solved the problem identified in #121, but a better long term solution of making them have arbitrary length was proposed.

An example of the syntax for creating an allocated character variable can be found here.

This is currently a low priority.