Merge pull request #2 from jiangzp/master

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Add camera calibration function. ( not integrated. )
Add listfilewithextension
use listFilesWithExtension in all code range.
Major update: add chessboard camera calibration functionality.
add calibration_chessboard.pdf
Merge pull request #7 from jiangzp/DuLi

Merge pull request #2 from jiangzp/master
Merge branch 'master' into gxgmy