install to $HOME/bin instead of /usr/local/bin, and ...

create symlinks instead of copying.
It'd be better to use symlinks, so in the future people can just run `git pull` and automatically update their database, without having to install it again.

Also, for most people, installing the cheat script to $HOME/bin will suffice. No need to install it to /usr/local/bin.
And I replaced string joining with `os.path.join`.

EDIT: also added columnized output, instead of a boring list, it now prints available cheatsheets as a funky column. bam.