rfq: add new RFQ service package

This commit adds a new package called rfq which contains the RFQ
service. Service sub-systems include:
1. Central service manager.
2. Quote price negotiator (and price oracle).
3. Peer message manager (stream handler).
4. HTLC order manager.

Author: ffranr

rfq/log.go

@@ -0,0 +1,26 @@
+package rfq
+
+import (
+	"github.com/btcsuite/btclog"
+)
+
+// Subsystem defines the logging code for this subsystem.
+const Subsystem = "RFQS"
+
+// log is a logger that is initialized with no output filters.  This
+// means the package will not perform any logging by default until the caller
+// requests it.
+var log = btclog.Disabled
+
+// DisableLog disables all library log output.  Logging output is disabled
+// by default until UseLogger is called.
+func DisableLog() {
+	UseLogger(btclog.Disabled)
+}
+
+// UseLogger uses a specified Logger to output package logging info.
+// This should be used in preference to SetLogWriter if the caller is also
+// using btclog.
+func UseLogger(logger btclog.Logger) {
+	log = logger
+}