adds unit tests for ShouldAlmostEqual
implements ShouldAlmostEqual
registers ShouldAlmostEqual
adds unit tests for ShouldNotAlmostEqual
implements ShouldNotAlmostEqual
registers ShouldNotAlmostEqual
correct ShouldAlmostEqual error messages and moves them to asserions/messages.go
Merge pull request #96 from aaasen/master

Adds ShouldAlmostEqual and ShouldNotAlmostEqual for float equality