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/memory/mmap_unix.go

@@ -0,0 +1,69 @@
+// Copyright 2011 Evan Shaw. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE-MMAP-GO file.
+
+// +build darwin dragonfly freebsd linux openbsd solaris netbsd
+
+// Modifications (c) 2017 The Memory Authors.
+
+package memory // import "modernc.org/memory"
+
+import (
+	"os"
+	"syscall"
+	"unsafe"
+)
+
+const pageSizeLog = 20
+
+var (
+	osPageMask = osPageSize - 1
+	osPageSize = os.Getpagesize()
+)
+
+func unmap(addr uintptr, size int) error {
+	_, _, errno := syscall.Syscall(syscall.SYS_MUNMAP, addr, uintptr(size), 0)
+	if errno != 0 {
+		return errno
+	}
+
+	return nil
+}
+
+// pageSize aligned.
+func mmap(size int) (uintptr, int, error) {
+	size = roundup(size, osPageSize)
+	b, err := syscall.Mmap(-1, 0, size+pageSize, syscall.PROT_READ|syscall.PROT_WRITE, syscall.MAP_SHARED|syscall.MAP_ANON)
+	if err != nil {
+		return 0, 0, err
+	}
+
+	n := len(b)
+	p := uintptr(unsafe.Pointer(&b[0]))
+	if p&uintptr(osPageMask) != 0 {
+		panic("internal error")
+	}
+
+	mod := int(p) & pageMask
+	if mod != 0 {
+		m := pageSize - mod
+		if err := unmap(p, m); err != nil {
+			return 0, 0, err
+		}
+
+		n -= m
+		p += uintptr(m)
+	}
+
+	if p&uintptr(pageMask) != 0 {
+		panic("internal error")
+	}
+
+	if n-size != 0 {
+		if err := unmap(p+uintptr(size), n-size); err != nil {
+			return 0, 0, err
+		}
+	}
+
+	return p, size, nil
+}