Added tiles2mrf script
Changes to spec for building on el7
Updated changelog, release bump
Merge pull request #23 from mike-mcgann/tiles2mrf

Added tiles2mrf script
Merge pull request #24 from mike-mcgann/el7

Updates for building on EL7
GIBS-540 Added EPSG code config for correct projection metadata in MRF.
Also renamed <resampling> to <overview_resampling>
and <resize> changed to <resize_resampling>
GIBS-561 Allow full paths in empty tile config
#19 GIBS-542 Added option and support for horizontal legends