Add percentile extension

Author: Daniël Sonck

README.md

@@ -174,6 +174,7 @@ go build -tags "icu json1 fts5 secure_delete"
 | JSON SQL Functions | sqlite_json | When this option is defined in the amalgamation, the JSON SQL functions are added to the build automatically |
 | Math Functions | sqlite_math_functions | This compile-time option enables built-in scalar math functions. For more information see [Built-In Mathematical SQL Functions](https://www.sqlite.org/lang_mathfunc.html) |
 | OS Trace | sqlite_os_trace | This option enables OSTRACE() debug logging. This can be verbose and should not be used in production. |
+| Percentile | sqlite_percentile | This option enables [The Percentile Extension](sqlite.org/percentile.html). |
 | Pre Update Hook | sqlite_preupdate_hook | Registers a callback function that is invoked prior to each INSERT, UPDATE, and DELETE operation on a database table. |
 | Secure Delete | sqlite_secure_delete | This compile-time option changes the default setting of the secure_delete pragma.<br><br>When this option is not used, secure_delete defaults to off. When this option is present, secure_delete defaults to on.<br><br>The secure_delete setting causes deleted content to be overwritten with zeros. There is a small performance penalty since additional I/O must occur.<br><br>On the other hand, secure_delete can prevent fragments of sensitive information from lingering in unused parts of the database file after it has been deleted. See the documentation on the secure_delete pragma for additional information |
 | Secure Delete (FAST) | sqlite_secure_delete_fast | For more information see [PRAGMA secure_delete](https://www.sqlite.org/pragma.html#pragma_secure_delete) |

sqlite3_opt_percentile.go

@@ -0,0 +1,15 @@
+// Copyright (C) 2019 Yasuhiro Matsumoto <mattn.jp@gmail.com>.
+// Copyright (C) 2018 G.J.R. Timmer <gjr.timmer@gmail.com>.
+//
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+//go:build sqlite_percentile
+// +build sqlite_percentile
+
+package sqlite3
+
+/*
+#cgo CFLAGS: -DSQLITE_ENABLE_PERCENTILE
+*/
+import "C"