BUG: Fix linkage for SmartPointerForwardReference for clang 4

Unifying SmartPointerForwardReference instantiation into a single
file.

This patched addressed linking issues with clang 3.0 when compiling
with shared libraries. Addresses the following linking error:

Undefined symbols for architecture x86_64:

  itk::SmartPointerForwardReference<itk::ProcessObject>::operator
  itk::ProcessObject*() const", referenced from:

Change-Id: Ib6d84681e677b47722c26a2ed698f1018c2b17a7
BUG: Fixing missing char type and doc for Thresholding filters

In C++ char, unsigned char, and signed char are distinct type. The
AutoMinMax IVAR for histogram based thresholds are now disabled for
char types. Also the documentation is corrected to match the code.

Change-Id: Ib4a3e47a6466980fd4f6d03e9e25baa63c8081c1
Merge branch 'release'

Change-Id: I2ccbf279522376dbab4bd20d6a24bd844feff2a0
COMP: Add missing itkVerson.h header.

to itkVersorTransformOptimizerv4.h.

Change-Id: Iadd4c325a17e7c23f2f612d208e2017355b6de1d
Merge topic 'versor-header'

bb5eea30 COMP: Add missing itkVerson.h header.
COMP: LBFGSOptimizerBasev4 explicit Doxygen link request.

Avoid "::" for documentation, which is interpreted by Doxygen a class member.

Change-Id: If06ed8674de0e065193126bda1f2f66a74181024
Co-authored-by: Ali Ghayoor <ali-ghayoor@uiowa.edu>
Merge topic 'FixAutoThreadholdAutoMinMax'

f85a46f6 BUG: Fixing missing char type and doc for Thresholding filters
Merge topic 'updatetransform-doxy'

4fb6c97a COMP: LBFGSOptimizerBasev4 explicit Doxygen link request.