Merge topic 'SIMPLEITK-521_AddToImageRegistrationMethod'

b299417e Adding MattesMutualInformation example and test
de68e6ff Adding MattesMutualInformation metric
Upgrade Superbuild version of PCRE to 8.35

Change-Id: Iac237505982ac18eae2db1ba5f6d53c6d077995e
Merge topic 'SIMPLEITK-545_UpgradePCRE' into next

adbe9895 Upgrade Superbuild version of PCRE to 8.35
0b2af3d1 Merge topic 'SIMPLEITK-521_AddToImageRegistrationMethod'