v0.1.1

ingot learns a registry

A version dependency now resolves out of Foundry, an index of TOML in a
git repository. A release records the commit to fetch and the tree it
must hash to, so resolving reaches the network for nothing but the index
and installing is checked against a hash rather than trusted to a host.

INGOT_REGISTRY names a registry, as a URL or as a directory; a directory
is used where it lies, which is what a private or offline registry is.
New verbs: update, search. `ingot add <name>` with no version records a
caret on the newest published one.