improved parsing of combinations and multithreading

combinations to be searched are now calculated before iterating
through them, so the need for checking each iteration is no longer
necessary. This has also allowed the multithreading to be fully
stacked even when the end of one file's permutations is reached,
as it just fills out iwht the next iteration on the second file.
added option to view common genes

also added hicluster's verbalise function for more flexible output
(including optional silencing of output from command line).
fixed bug in verbalise function

the concatenation of strings would return an error if one of the
items was not a string. Now the function converts all items
passed to it into strings, before concatenation.