Basilisk v2.1.6

• Refactored :ref:keplerianOrbit to not depend on the gravityEffector class
• Updated Basilisk install documentation to discuss accessing source code from GitHub.com
• Fixed an issue where attaching a thruster to a body different than the hub when using zeroBase would yield very large offsets.
• Added documentation in :ref:bskPrinciples-4 on how to read the current message values
• Highlighted the challege of setting up a recorder on a re-directed message in :ref:bskPrinciples-7
• added the ability to add a recorder() to a C-wrapped module input message
• Fix an issue in in :ref:magneticFieldWMM where a fixed width array holding a file path would result in a cutoff
  path when basilisk is located in a directory path of greater than 100 characters.
• Updated the build system to use newer versions of eigen, protobuf, cppzmq
  and opencv. This corrects some build issues with new compilers.
• The linearAlgebra, rigidBodyKinematics, orbitalMotion were mistakenly exposed as part of the
  :ref:sim_model module's API. They have been removed and the functions they provided are still found in
  Basilisk.utilities.orbitalMotion, Basilisk.architecture.linearAlgebra, and
  Basilisk.architecture.rigidBodyKinematics.
• Fixed an issued recording the timeWritten information of a C-wrapped message
  with a recorder() module.
• Updated :ref:pullCloneBSK to ask the user to first install lfs before pulling a copy
  of the Basilisk repo due to some large files being stored in the GitHub large file storage
  system.
• Updated :ref:scenarioGroundLocationImaging to properly save off the ground location
  information for Vizard
• Added a new helper function to convert C arrays to Eigen::MRPd and vice-versa inside avsEigenSupport.
• Updated :ref:spinningBodyStateEffector to use the :ref:HingedRigidBodyMsgPayload output message type for compatibility with other modules
• Added the ability to set an inertial heading in the :ref:boreAngCalc module. Changed the internal module logic to use Eigen library variables and functions instead of C-style arrays and methods.
• Added support for Vizard v2.1.3
• Updated :ref:simpleInstrumentController to provide the option to consider the angular velocity tracking error norm
  when considering to take an image.