Updates to masking and some I/O functionality

Updated README to show users how to install dependencies

Moved getMask to its own .R file

added mergeLabels and some I/O code from demo

Added a style guide for developers to doc/source, but I'm not sure
how to include this in the web page
Merge remote-tracking branch 'origin/master' into cookpa
Merge remote-tracking branch 'origin/master' into cookpa