Add IDateTimeFluentAssertion

Note that comparing Utc date kind with local date kind works like a
charm
Update ReadMe.md
Replaces Verifies that by Checks that within the INumberFluentAssertion methods comments.
Rename HaveSome for IsSameAs

Change "Verifies that" for "Check that"
Make some unit test more fluent by usgin variable name like christmas
Fix Checks Typo (Replace Check for Checks)
Fix typo, stylecop rules and coverage to 100%
Fix Typo again and again :-(
Add IBooleanFluentAssertion
Fix unit test related to time zone conversion
Includes the new CONTRIBUTING.md file.
Updates the Contributing.md file.
Indicates that Apache 2.0 license header is not mandatory for unit test
files.
Improves both the Readme and CONTRIBUTING md files.
Emphases the Dev DoD within the CONTRIBUTING.md
Add the Date Kind in string formatting
Make Date Comparison respect the .NET Framework
Introduces the spike suggested by Rui in order to introduce extension-method-based extensibility for NFluent (code of the spike is in the unit test project).
Renames most of the ExtensionSpike types.
Renames some files of the Spike, and tries to make the ExtensionSpikeTests.DoNotThrowExceptionWhenSutIsASubTypeOfTheTypeReferencedInTheExtensionMethod() pass (failure so far ... ;-(
Renames a test of the Spike.