gitignore: remove unused entries

The bin entry were shadoing an existing directory. I would much prefer
to add patterns to .gitignore on a per-case basis when we need them.
gitignore: ignore editor backup files
Add command line help epilog

This adds an epilog to the --help output to show the user how to get
detailed help about a specific command. Example:

$ zpm bundle --help
or
$ zpm new --help
Merge pull request #10 from mgeisler/ignore

Amended .gitignore
Merge pull request #11 from larsbutler/improve-cli-usage-help

Add command line help epilog