Ensure proper attribution and license conformance

#### From [`rebar3`](https://github.com/erlang/rebar3)
- `gitignore` is directly copied
- `library/lfe_lib.template` is a slightly modified version of rebar3's `lib.template`
- `library/otp_lib.app.src` is slightly modified
### From [`lfetool`](https://github.com/lfex/lfetool)
- `library/README.md` is slightly modified
