docs: refer to standalone MetricsQL package

docs/ExtendedPromQL.md

@@ -2,6 +2,7 @@
 
 VictoriaMetrics implements MetricsQL - query language inspired by [PromQL](https://prometheus.io/docs/prometheus/latest/querying/basics/).
 It is backwards compatible with PromQL, so Grafana dashboards backed by Prometheus datasource should work the same after switching from Prometheus to VictoriaMetrics.
+[Standalone MetricsQL package](https://godoc.org/github.com/VictoriaMetrics/VictoriaMetrics/lib/metricsql) can be used for parsing MetricsQL in external apps.
 
 The following functionality is implemented differently in MetricsQL comparing to PromQL in order to improve user experience:
 * MetricsQL takes into account the previous point before the window in square brackets for range functions such as `rate` and `increase`.

lib/metricsql/doc.go

@@ -1,6 +1,6 @@
 // Package metricsql implements MetricsQL parser.
 //
-// This parser can parse PromQL. Additionally it can parse MetricsQL extensions.
+// This parser can parse PromQL. Additionally it can parse all the MetricsQL extensions.
 // See https://github.com/VictoriaMetrics/VictoriaMetrics/wiki/ExtendedPromQL for details about MetricsQL extensions.
 //
 // Usage:
@@ -10,6 +10,6 @@
 //        // parse error
 //    }
 //    // Now expr contains parsed MetricsQL as `*Expr` structs.
-//    // See metricsql.Parse examples for more details.
+//    // See Parse examples for more details.
 //
 package metricsql

lib/metricsql/parser.go

@@ -9,6 +9,8 @@ import (
 
 // Parse parses MetricsQL query s.
 //
+// All the `WITH` expressions are expanded in the returned Expr.
+//
 // MetricsQL is backwards-compatible with PromQL.
 func Parse(s string) (Expr, error) {
 	var p parser