[Vision] Locate AR Markers about qi-table

[GavinPHR]

can recognize AR markers successfully when image/video quality is good

have some difficulty when quality is poor and when objects are moving

[GavinPHR]

Have tested the system in the SDP arena. The AR markers (of varies size) were printed on an A4 paper and the paper was placed about 10 cm above the ground. As long as the AR marker is bigger than 6cm-by-6cm, the system can return the coordinates quite consistently. Currently trying to clean up code and design the API.

[GavinPHR]

Currently, a new video feed is started every time a set of coordinates are requested. It is quite slow (2 seconds) to start a new video feed every time and we obviously don't want that. I am thinking about having a video capture always running in the background and do recognition when requested. Not quite sure how to implement it elegantly as of now.

[GavinPHR]

now added exception handling and a small usage guide.
merge for code review

[stormwindy]

Closed by #9