Fixes to RemovePrivateMembersProcessor and others.

Added some CecilExtensions: EmitBaseCallWithDefaultArgumentValues,
EmitPushDefaultArgumentValues, GetBaseConstructorCalls,
GetParameterlessConstructor, MakeGenericInstanceType,
AsMethodOfGenericTypeInstance, WithGenericTypeArguments.
Added CloneExtensions: .Clone() methods for some Cecil classes.
Improved RemoveMethodBodiesProcessor. It now tries to call the
parameterless base constructor and only falls back to other methods if
it's not found.
RemovePrivateMembersProcessor can now remove internal constructors (with
parameters) if the class has a parameterless constructor.