Fix missing hex_val conversions

In the mosaic squares pattern, vals were being sent as strings from
the hash without being converted to numeric form first. When val > 9,
for examples, opacity incorrectly ends up at its minimum value 37.5%
of the time.
Merge pull request #26 from btmills/master

Fix missing hex_val conversions
bump to v1.1.3
add link to GitHub Guides