Bug Fixes

I've changed a few things and put it together into one pull request

* Current version on github is broken, instead of printing 'command' it simply prints a function if the command variable does not exist in the package.json, this causes the bash file to be invalid. So checks whether the command is something funky (like a function) and uses the default if that's the case
* Updated the readme to include the command option that was added in a previous pull request
* Added ability to specify the location of forever. This is important when using something like https://www.npmjs.org/package/nvm because forever is not in /usr/local/forever, it's in some different location. Also added this to readme
* Added quotes around bash variables, this should prevent any problems where passed arguments have spaces in the paths
* Fixed some warnings/errors when using Ubuntu 14.04. No longer needs the start-daemon line