Fix compilation warnings with GCC 9.1

[jslee02]

• Fix redundant use of std::move() in return statement
• Obey the rule of three when the custom copy constructor is defined

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• Document new methods and classes
• Format new code files using clang-format

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• Set version target by selecting a milestone on the right side
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[codecov]

Codecov Report

Merging #1366 into master will decrease coverage by 0.02%.
The diff coverage is 45.28%.

@@            Coverage Diff             @@
##           master    #1366      +/-   ##
==========================================
- Coverage   56.92%   56.89%   -0.03%     
==========================================
  Files         366      366              
  Lines       27341    27387      +46     
==========================================
+ Hits        15563    15581      +18     
- Misses      11778    11806      +28

Impacted Files	Coverage Δ
dart/dynamics/detail/PlanarJointAspect.hpp	100% <ø> (ø)	⬆️
dart/common/sub_ptr.hpp	100% <ø> (ø)	⬆️
...art/dynamics/detail/TranslationalJoint2DAspect.hpp	50% <ø> (-10%)	⬇️
dart/collision/bullet/BulletCollisionDetector.cpp	70.15% <0%> (ø)	⬆️
dart/dynamics/detail/GenericJointAspect.hpp	50% <0%> (-35.19%)	⬇️
dart/dynamics/detail/BodyNodePtr.hpp	93.67% <100%> (+0.24%)	⬆️
dart/dynamics/detail/PlanarJointAspect.cpp	86.88% <100%> (+3.21%)	⬆️
dart/utils/VskParser.cpp	72.13% <100%> (ø)	⬆️
dart/common/detail/sub_ptr.hpp	95.65% <100%> (+0.41%)	⬆️
...art/dynamics/detail/TranslationalJoint2DAspect.cpp	32.05% <50%> (+3.26%)	⬆️
... and 4 more