Merge pull request #22 from tarebyte/master

Adding uri to background-image example
bump to v1.1.0
check requested pattern against list
fix reading beyond hash length

In the concentric circles and nested squares patterns, when `i = 0`
i.e. the top left corner of the pattern, `val` for the inner shape is
read from `hash[40]`, but the hash itself is only 40 characters long.
Merge pull request #24 from btmills/master

fix reading beyond hash length
remove rescue block
Merge pull request #23 from jasonlong/generator-validation

Make sure requested pattern is valid
bumped version to 1.1.1