Log Message:
Update to 0.18:

0.18
 * Mark most of unstable API as stable
 * Bump Glib dependency (2.38+)
 * Add secret_service_encode_dbus_secret() and decode functions
 * Use TAP for testing, parallel tests, and non-recursive make
 * Updated FSF's address
 * Remove unstable vapi [#721429]
 * Build fixes [#720087 #720244 #707452]
 * Updated translations