Merge branch 'docu_calibration' into 'master'

docs/source/calibration/extrinsic_calibration.md

docs/source/calibration/images/demo_points.3dc

docs/source/calibration/images/extrinsic_all_enlarged.png

docs/source/calibration/images/extrinsic_grid_and_points.png

docs/source/calibration/images/extrinsic_select_points.png

...urce/calibration/images/intrinsic_calibration_section.png

docs/source/calibration/images/photothumb.db

docs/source/calibration/images/points.png

docs/source/calibration/images/pre_post_intrinsic.jpg

docs/source/calibration/intrinsic_calibration.md

docs/source/planning/calibration.md

docs/source/planning/camera.md

docs/source/planning/images/calibration_examples.jpg

docs/source/planning/images/chessboard.jpg

docs/source/planning/images/chessboard_border.jpg

docs/source/planning/images/chessboard_coverage.jpg

docs/source/planning/images/coordinate_grid.png

docs/source/planning/images/ranging_pole_level.png

docs/source/planning/planning.md