Fix smooth triangles catmark weights

- rename enums in sdc/options
- add support for "smoothtriangles" tag in Shapes
- add 2 test shapes to glViewer
Fix error string conversion to use swtich statement (safer)
Fix tutorial include paths

- now prettier with <opensubdiv> prefix
Merge remote-tracking branch 'upstream/dev' into dev
Rename Sdc::Options vertex boundary interpolation rule enums

- VVarBoundaryInterpolation is now VtxBoundaryInterpolation
- enum prefix change from VVAR to VTX
- generel cleanup / doxyfication
- update of beta / release notes
Rename some members of Far::TopologyRefinerFactory::TopologyDescriptor for consistency

- propagate changes to tutorials / examples
Refactor Vtr::Array for better "const" safety

Const' declared instances of Vtr::Array do not protect the pointer held
privately by the class properly. In order to force the compiler to
protect this pointer, we removed all non-const accessors from Vtr::Array
(now renamed Vtr::ConstArray) and moved them to a child class (Vtr::Array),
which requires const_cast<> operators internally to allow access.

The change & renaming is then propagated to all internal dependencies.
Fix Windows build
Fix Png dependency in examples build (fixes screenshot ability in glViewer)
Update subdivision ReST documentation to match changes in Sdc
Fix typo in sdc/options.h
Update release notes & documentation for upcoming Beta release
Fix infinitely sharp edges isolation

- change topology refiner to check for edge sharpnesses when selecting faces for isolation
- add face-aggregator for edge tags to Vtr::Level
- fix logic in Far::PatchTablesFactory to correctly tag single-crease patches along infinitely sharp edges

note : this fix is a bit of a cludge - barfowl confirms that the vertex crease tags (VTags) are intended to
carry neighborhood information, which they currently do not. we will revisit this shortly and fix the tags,
which will allow us to simplify the traversal logic when isolating topology features.

fixes #369
Fix build warning in far_tutorial_1
Add glfw error callback to code examples
Remove outdated OVERVIEW.txt files

- contents have been moved to ReST documentation
Fix doxy comments in Far::TopologyRefiner
Remove obsolete code path in Far::TopologyRefiner (_VTR_COMPUTE_MASK_WEIGHTS_ENABLED)
WIP doxyfication of Sdc
Remove Hbr from doxygen docs