Adds README file with simple explanation and example of the library
Adds super simple example of how to use this in an activity
Adds 2 examples showing how to use this library:

 - The first one is the simple example which only sets the text to share
 - The second one shows how to use all the available properties for sharing
Extracts listener to filed
Adds `priority-share` to the activity label
Gets rid of MRU acronyms and writes the full thing
Adds targets to README and to simple activity
Renames for consistency
Fixes case in strings and adds a better description for the text to share
Adds translatable=false to the non translatable string
Renames method to explain better what it does
Adds more descriptive summary text to the README
Uses full names instead of just an acronym
Merge pull request #9 from novoda/priority_share_readme_and_demo

Priority share - add readme and demo project