Initial plugin implementation

* refactor packages, flags, subscriptions
* DRY refactor builder tests
* use mockgen to generate mocks
* update README
* MODE=statediff no longer needed for unit tests
* simplify func names, clean up metrics
* move write params to service field
* sql indexer: confirm quit after ipld cache reset
  prevents negative waitgroup panic
* don't let TotalDifficulty become nil
* use forked plugeth, plugeth-utils for now

utils/log/log.go

@@ -0,0 +1,73 @@
+package log
+
+import (
+	// geth_log "github.com/ethereum/go-ethereum/log"
+	"github.com/inconshreveable/log15"
+	"github.com/openrelayxyz/plugeth-utils/core"
+)
+
+type Logger = core.Logger
+
+var (
+	DefaultLogger core.Logger
+
+	TestLogger = Log15Logger()
+)
+
+func init() {
+	// The plugeth logger is only initialized with the geth runtime,
+	// but tests expect to have a logger available, so default to this.
+	DefaultLogger = TestLogger
+}
+
+func Trace(m string, a ...interface{}) { DefaultLogger.Trace(m, a...) }
+func Debug(m string, a ...interface{}) { DefaultLogger.Debug(m, a...) }
+func Info(m string, a ...interface{})  { DefaultLogger.Info(m, a...) }
+func Warn(m string, a ...interface{})  { DefaultLogger.Warn(m, a...) }
+func Crit(m string, a ...interface{})  { DefaultLogger.Crit(m, a...) }
+func Error(m string, a ...interface{}) { DefaultLogger.Error(m, a...) }
+
+func SetDefaultLogger(l core.Logger) {
+	// gethlogger, ok := l.(geth_log.Logger)
+	// if !ok {
+	// 	panic("not a geth Logger")
+	// }
+	DefaultLogger = l
+}
+
+// Log15Logger returns a logger satisfying the same interface as geth's
+func Log15Logger(ctx ...interface{}) wrapLog15 {
+	return wrapLog15{log15.New(ctx...)}
+}
+
+type wrapLog15 struct{ log15.Logger }
+
+func (l wrapLog15) New(ctx ...interface{}) Logger {
+	return wrapLog15{l.Logger.New(ctx...)}
+}
+
+func (l wrapLog15) Trace(m string, a ...interface{}) {
+	l.Logger.Debug(m, a...)
+}
+
+func (l wrapLog15) SetLevel(lvl int) {
+	l.SetHandler(log15.LvlFilterHandler(log15.Lvl(lvl), l.GetHandler()))
+}
+
+// New returns a Logger that includes the contextual args in all output
+// (workaround for missing method in plugeth)
+func New(ctx ...interface{}) Logger {
+	return ctxLogger{DefaultLogger, ctx}
+}
+
+type ctxLogger struct {
+	base Logger
+	ctx  []interface{}
+}
+
+func (l ctxLogger) Trace(m string, a ...interface{}) { l.base.Trace(m, append(l.ctx, a...)...) }
+func (l ctxLogger) Debug(m string, a ...interface{}) { l.base.Debug(m, append(l.ctx, a...)...) }
+func (l ctxLogger) Info(m string, a ...interface{})  { l.base.Info(m, append(l.ctx, a...)...) }
+func (l ctxLogger) Warn(m string, a ...interface{})  { l.base.Warn(m, append(l.ctx, a...)...) }
+func (l ctxLogger) Crit(m string, a ...interface{})  { l.base.Crit(m, append(l.ctx, a...)...) }
+func (l ctxLogger) Error(m string, a ...interface{}) { l.base.Error(m, append(l.ctx, a...)...) }