Added the CS0649 pargma to suppress the warning.
Introduced the TestArgumentCollection class.
Slightly refactored the TestArgument class,

which is to introduce the Specified property.
Coverted the Argument property to the method.
Slightly refactored the TestArgument class.
Added the omitted test.
Refactored many classes.
Introduced the FlagsExtensions class.
Refactored InjectingCustomization

to extract the registered types.
Slightly refarctored InjectingCustomization.
Refactored some classes.
Added the test method

to test that the As property ignores the Matches value for type, such as
BaseClasses and ImplementedInterfaces, but not for name, such as
ParameterName, PropertyName and FieldName.
Refactored CustomizationCollection

to extract the method.
Refatored to remove the middle man

 - the Parameter property.
Slightly refactored to order the method.
Renamed the classes.
Slightly refactored.
Revert "Renamed BaseClass to BaseClasses"

This reverts commit 9db576e6c1239fa19f6c325a0989ae307dae32b1.

Conflicts:
	src/AutoFixture.Contrib/Xunit/SpecAttribute.cs
Incremented patch version,

to indicate that this the BaseClasses value of the Matches enum was
renamed to BaseClass. This actually causes breaking change but as this
is trivial matter, the patch version was incremented.