Add --max-size flag to limit size of repositories (#72)

* Add --max-size flag to limit repository size

* Only update repo size on successful write

* Use initial size as current size for first SaveBlob

* Apply LimitReader to request body

* Use HTTP 413 for size overage responses

* Refactor size limiting; do checks after every write

* Remove extra commented lines, d'oh

* Account for deleting blobs when counting space usage

* Remove extra commented line

* Fix unrelated bug (inverted err check)

* Update comment to trigger new CI build

cmd/rest-server/main.go

@@ -41,6 +41,7 @@ func init() {
 	flags.BoolVar(&server.Debug, "debug", server.Debug, "output debug messages")
 	flags.StringVar(&server.Listen, "listen", server.Listen, "listen address")
 	flags.StringVar(&server.Log, "log", server.Log, "log HTTP requests in the combined log format")
+	flags.Int64Var(&server.MaxRepoSize, "max-size", server.MaxRepoSize, "the maximum size of the repository in bytes")
 	flags.StringVar(&server.Path, "path", server.Path, "data directory")
 	flags.BoolVar(&server.TLS, "tls", server.TLS, "turn on TLS support")
 	flags.StringVar(&server.TLSCert, "tls-cert", server.TLSCert, "TLS certificate path")