Add 'bin' section to package.json
Rename 'src' dir to 'lib'
Ignore vim swap files
Modify files to better match de-facto npm standards

This commit makes better use of npm's package.json file to
provide better support for using hpd. For example, 'npm start' now
maps to the hpd binary, and 'require('hpd')' will let you start/stop
the server from other scripts.