Add SQLite support, fix un-thread-safe DB caches, small performance f… (#172)

* Add SQLite support, fix un-thread-safe DB caches, small performance fixes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add SQLite licenses to README

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* appease the linter, and fix my dumbass-ery

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* make requested changes

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

* add back comment

Signed-off-by: kim (grufwub) <grufwub@gmail.com>

vendor/modernc.org/sqlite/sqlite_go18.go

@@ -0,0 +1,48 @@
+// Copyright 2017 The Sqlite Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.8
+
+package sqlite // import "modernc.org/sqlite"
+
+import (
+	"context"
+	"database/sql/driver"
+)
+
+// Ping implements driver.Pinger
+func (c *conn) Ping(ctx context.Context) error {
+	_, err := c.ExecContext(ctx, "select 1", nil)
+	return err
+}
+
+// BeginTx implements driver.ConnBeginTx
+func (c *conn) BeginTx(ctx context.Context, opts driver.TxOptions) (driver.Tx, error) {
+	return c.begin(ctx, opts)
+}
+
+// PrepareContext implements driver.ConnPrepareContext
+func (c *conn) PrepareContext(ctx context.Context, query string) (driver.Stmt, error) {
+	return c.prepare(ctx, query)
+}
+
+// ExecContext implements driver.ExecerContext
+func (c *conn) ExecContext(ctx context.Context, query string, args []driver.NamedValue) (driver.Result, error) {
+	return c.exec(ctx, query, args)
+}
+
+// QueryContext implements driver.QueryerContext
+func (c *conn) QueryContext(ctx context.Context, query string, args []driver.NamedValue) (driver.Rows, error) {
+	return c.query(ctx, query, args)
+}
+
+// ExecContext implements driver.StmtExecContext
+func (s *stmt) ExecContext(ctx context.Context, args []driver.NamedValue) (driver.Result, error) {
+	return s.exec(ctx, args)
+}
+
+// QueryContext implements driver.StmtQueryContext
+func (s *stmt) QueryContext(ctx context.Context, args []driver.NamedValue) (driver.Rows, error) {
+	return s.query(ctx, args)
+}