print method for remotes class

Closes #32

Simple, but I like how it looks:

```
❯ r
<remotes>
- refs: `eisa`, `r-lib/usethis`, `dplyr`, `purrr`, `foobar`, `xxx`,
    `yyy`, `qqq`
- library: `/tmp/lib`
- has resolution, with errors
- has solution, with errors
```