fix dropped "+" when 0 passed as vertical roll amt

fix dropped "+" when 0 passed as vertical roll amt
Add highlight-style support
add highlightStyle options in tests
Add tolerance to gm.compare options object. Change the gm.compare logic to always run the mse comparison as expected.
Merge pull request #258 from Vokkim/master

Add tolerance to gm.compare options and always perform MSE comparison
gm.compare: support for return values like 9.51582e-05
added test for compare
release 1.15.0
Add highlight-style support
add highlightStyle options in tests
fix tests after rebase
update readme
Merge pull request #272 from fdecampredon/master

Add highlight-style support in compare
Merge pull request #267 from dwtkns/patch-1

fix dropped "+" when 0 passed as vertical roll amt
release 1.16.0
readme