Update the copyright, assign it to thoughtbot

This is a thoughtbot project now, so assign copyright to thoughtbot.
Add a hostname override

Based on issue #82, we now provide `-B` to override the hostname. In
particular:

- `mkrc -B foo` will enable `-o` but with the hostname set up `foo`.
- `lsrc -B foo` will work like normal `lsrc` except it treats `host-foo`
as the host-specific directory.
- `rcup -B foo` will run a normal `rcup` except `host-foo` is the
host-specific directory.
- `rcdn -B foo` is just like normal `rcdn`, but with `host-foo` as the
  host-specific directory.
Document the -B flag
Configure HOSTNAME in the rcrc(5)

Add a `HOSTNAME` option for rcrc(5), which can be overridden by `-B`.
Update the NEWS