Add tests around the examples shown on the shouldly.github.io documentat...

...ion site

Addresses some concerns raised in #111

Tests for each documented example is grouped together via a container class. The syntax and error message generated should be compared with and used with Shouldly's documentation. Both the NUnit and Shouldly tests are shown where applicable.

Each group also includes happy path tests showing a passing assertion. The happy path for collections is current failing (#100) so this should probably be merged after that issue is resolved, not before.