Add human hg38 genome file

Created with the UCSC fetchChromSizes [1] tool:

    fetchChromSizes hg38 > genomes/human.hg38.genome

[1] http://hgdownload.cse.ucsc.edu/admin/exe/linux.x86_64/fetchChromSizes
Merge pull request #107 from martijnvermaat/hg38

Add human hg38 genome file