api/auth: create AuthenticatorFunc type, replacing AuthMethod interface
api/auth/nil: initial commit, to simplify logic for unauthenticated routes
core/apiRouter: call Authenticate method on AuthenticatorFunc, for single entry point
Inject current git revision on build, expose it over HTTP at /revision
manager: move git commit revision injection to core.Revision
config: add a Help() method to provide information on configuration failures
core/manager: provide help on invalid media folder, do not die on empty git revision
Makefile: add install target
README: update documentation regarding Makefile
web/index: update index with shameless plug for web UI help
README: add FAQ about web UI
Merge branch 'master' into dev_taggolib