Added Swap and AbstractBuilder and their tests.
Added IPool, AbstractPool and its test.
Added some more extension methods for IEnumerable<T> and tests.
Added some extension methods to ListExtension.
Added NumberExtension ands test.
Added TypeExtension and test.
Added AssemblyExtension.
Added IEnvironmentVariableProvider its implementation and tests.
Added some missing test for EnvironmentVariableProvider.
Added ISealable, its implementation and test.
Added ICache, one implementation and test.