move from packages to node_modules

change the directory name to support the jpm switch
update the package.json for jpm

include a main, repository, and update the dependencies attribute
pathfinder is now addon-pathfinder

update require location
making the dependencies versions explicit, otherwise a simple api change can break this add-on
using require to import JSMs
Closes #109 Show All Bookmarks was showing about:history :(
Updating the README.md build instructions