Fix variable names and add dryrun
Refactor bootstrap.sh for readability

Shamelessly stole some code back from mtarbit/dotfiles for bootstrap.sh.
Handling of commands and switches is much more readable and intelligent now.
Update gitignore to include sandbox folder
Check if $HOME/bin exists before symlinking bins

Fixes #6.
Bootstrap.sh install inits git submodules

Git submodules are now initialized when bootstrap.sh install is called.
Another feature shamelessly grabbed from mtarbit/dotfiles.