Added a new mapping expression - IgnoreAllPropertiesWithAnInaccessibleSetter()

IgnoreAllPropertiesWithAnInaccessibleSetter() supports scenarios where the destination type contains several properties with private or protected setters that should not be mapped from the source type.

I added a test class with four "facts" for this, and they all pass. I also added summary documentation.

This addresses https://github.com/AutoMapper/AutoMapper/issues/187 (and it appears to be related to https://github.com/AutoMapper/AutoMapper/issues/173 and https://github.com/AutoMapper/AutoMapper/issues/218).

(Note: I previously submitted a pull request with a different solution involving an overload to AssertConfigurationIsValid(), but I believe this is a better solution because it allows more fine-grained control and doesn't make any existing methods obsolete. I also managed not to screw up the line endings this time :))