Encode signed global id metadata with a hash.

Let's us accommodate new metadata without breaking old messages.

This change also flips some `assert_equal` calls with wrong ordered arguments.
require activesupport in railtie
Merge pull request #32 from seuros/master

Explicitly require Active Support before cherry-picking core extensions.
Use string keys in to_h.
Merge pull request #31 from kaspth/hash-metadata

Encode signed global id metadata with a hash.
Expiration for signed global ids.
Merge pull request #29 from kaspth/signing-expiration

Expiration for signed global ids.
Passing nil expires_at turns off expiration checking.
Merge pull request #33 from kaspth/nil-expires-at

Passing nil expires_at turns off expiration checking.