rename gc content function to get_gc_for_genome
rename gc content function to get_gc_for_genome

The name better describes how the function is being called.

asherkhb/coge,LyonsLab/coge,LyonsLab/coge,asherkhb/coge,asherkhb/coge,LyonsLab/coge,LyonsLab/coge,LyonsLab/coge,asherkhb/coge,asherkhb/coge,asherkhb/coge,asherkhb/coge,LyonsLab/coge,LyonsLab/coge,LyonsLab/coge,LyonsLab/coge,asherkhb/coge,asherkhb/coge