Issue #49. Create command line option for canvas width and height.

Changes are verified. It can be merged to master. 
1. As we used most of the characters for command line options, i just kept as '/0' for these two options as of now. 
2. Also we are currently having default width and height as 800,400 can we default it to the screen size of device/PC. 

Please give your comments on the above.