feature: native option

Author: Simone Sanfratello

README.md

@@ -96,9 +96,10 @@ fastify.listen(3000, err => {
 As you can see there is no need to close the client, since is done internally. Promises and async await are supported as well.
 
 ### Native option
-Use native libpq to gain high performance; it will use [pg-native](https://github.com/brianc/node-pg-native) instead of [pg](https://github.com/brianc/node-pg).  
+Use native `libpq` to gain high performance; it will use [pg-native](https://github.com/brianc/node-pg-native) instead of [pg](https://github.com/brianc/node-pg).  
 Note: it requires PostgreSQL client libraries & tools installed, see 
-[instructions](https://github.com/brianc/node-pg-native#install).
+[instructions](https://github.com/brianc/node-pg-native#install).  
+Note: trying to use native options without successfully installation of `pg-native` will get a warning and fallback to regular `pg` module.
 
 ```js
 const fastify = require('fastify')

index.js

@@ -5,8 +5,9 @@ let pg = require('pg')
 
 function fastifyPostgres (fastify, options, next) {
   if (options.native) {
+    delete options.native
     if (!pg.native) {
-      console.warn('pg-native not installed, can\'t use native option')
+      console.warn('pg-native not installed, can\'t use native option - fallback to pg module')
     } else {
       pg = pg.native
     }