PR for issue #3

This branch is built upon the latest version of pyswatch and hence has a few more changes than described in issue #3 (closed). It also removes duplication of calling function : compareBufferWithRef by modifying swatch/cli/board_data/main_compare. This change had to be done since main_compare is wrapped inside click function. In addition, in order to create the image, I have followed the exact instructions at the moment as described. However, it might need a few more as I can see (e.g. setup.py etc) but can be discussed in this PR.