add richer operators for testing interval membership
Generalize symbolic set operators a bit.

Previously they were defined in Interval.scala but lived in the
spire.optiona.unicode package. Now, the implicit class has been
moved there, and a companion class for Set[A] has been added as
well.
very minor GUIDE typo
Add ZigguratBenchmarks to compare performance of Polar Method v.s. Ziggurat algorithm
Add Generator#nextGaussian Polar method to benchmarks
Merge pull request #270 from dusank/topic/ZigguratBenchmarks

Add ZigguratBenchmarks to compare performance of Polar Method v.s. Ziggu...
Fix typos, Remove unused imports
Merge pull request #271 from dusank/topic/Fix-typos-and-imports

Fix typos, Remove unused imports
Merge pull request #268 from non/topic/more-unicode

Topic/more unicode
Merge commit '356ce2cae66dd052aa85fedfe2eca5c8e149e909'