cad/openvsp: update to 3.20.0

ChangeLog: http://openvsp.org/blogs/announcements/2019/12/29/openvsp-3-20-0-released

Features:

• Smart Input for simple math in input boxes
• API examples in documentation
• Draw cg from mass prop screen
• CEDIT improvements
• Make wing section projected area an output Parm
• Add get parent/child to API
• Fix VSPAERO crash for Uber CRM example case
• Lots of cleanups identified through static analysis
• Travis deployment
• Update Travis MacOS build to match release builds

Library Updates:

• Include expparse simple expression parsing library

Bug Fixes:

• Don't crash structures STEP/IGES output when no structure defined
• Parasite drag for identically named geoms
• DegenGeom crash when subsurfaces extended beyond [0,1]
• CEDIT fixes