Also define a handful of utility methods:
- `New(owner, repo)`
- `FullName`: the name slash owner pair
- `FromFullName`: parse the name slash owner pair
- `FromURL`: parse a GitHub.com URL
- `IsSame(r1, r2)`: compare two repositories
- The local git remotes are scanned and resolved to GitHub repositories
- The "base" repo is the first result resolved to its parent repo (if a fork)
- The name of the default branch is read from the base repo
- The "head" repo is the first repo that has push access
This is for symmetry with `issue list`.
The problem is that the `Repository.pullRequests` connection doesn't
support filtering by assignee, therefore we need to switch to search API
in case an assignee was specified. This is awkward, but I don't see
another way.
When on a `patch-1` branch locally, `gh pr view` would happily open the
first open PR it finds with "patch-1" as its head, even those coming
from forks.
