Enable "hidden" visibility to reduce wheel size

[blowekamp]

The current wheel size is nearly 50MB for 64-bit linux. This is the size limit of PyPi. With correctly specified hidden visibility flags, the size can be reduce to ~38MB.

Previous release were manually configured with:

  CMAKE_CXX_FLAGS:STRING=-fvisibility=hidden -fvisibility-inlines-hidden
  CMAKE_C_FLAGS:STRING=-fvisibility=hidden

The newer strategy has been to use the related CMake visibility presets. Correctness with the recent changes in ITK and how SimpleITK interacts with these properties needs to be tests and reviewed in the current SimpleITK master.

It is planned that explicitly setting the following would be best:

 -DCMAKE_VISIBILITY_INLINES_HIDDEN:BOOL=ON
 -DCMAKE_C_VISIBILITY_PRESET:STRING=hidden
 -DCMAKE_CXX_VISIBILITY_PRESET:STRING=hidden

This is under the assumption that the packaging only produces a single shared library.

[blowekamp]

Recent commits in SimpleITK should improve hiding of symbols:
SimpleITK/SimpleITK@70470a7

Need to update the package version and determine the size of the package distribution.

[blowekamp]

Additionally, the Python Library was not being stripped of symbols.
Pull request #19 adresses the stripping issue.