fix panic when reflecting on maps (tinylib#181)

```
package main

//go:generate msgp

import (
	"bytes"
	"fmt"
	"os"

	"github.com/tinylib/msgp/msgp"
)

type Feedback map[string]interface{}

func main() {
	deepMap := make(map[string]map[string]string)
	feedback := Feedback{"general": deepMap}

	bb := new(bytes.Buffer)
	if err := msgp.Encode(bb, feedback); err != nil {
		fmt.Fprintf(os.Stderr, "%s\n", err)
		os.Exit(1)
	}
	fmt.Printf("%#v\n", bb.Bytes())
}

// 1. Type `go generate main.go`.
// 2. Type `go run main.go main_gen.go`.
```

fix panic when reflecting on maps (tinylib#181)

```
package main

//go:generate msgp

import (
	"bytes"
	"fmt"
	"os"

	"github.com/tinylib/msgp/msgp"
)

type Feedback map[string]interface{}

func main() {
	deepMap := make(map[string]map[string]string)
	feedback := Feedback{"general": deepMap}

	bb := new(bytes.Buffer)
	if err := msgp.Encode(bb, feedback); err != nil {
		fmt.Fprintf(os.Stderr, "%s\n", err)
		os.Exit(1)
	}
	fmt.Printf("%#v\n", bb.Bytes())
}

// 1. Type `go generate main.go`.
// 2. Type `go run main.go main_gen.go`.
```

apply pragmas to unmarshal printer (tinylib#176)

* fix issue 174: apply pragmas to unmarshal printer

* fix build on tip; time.Time representation has changed

use go1.7 as base

Merge pull request tinylib#135 from tianon/386

Add some explicit type declarations to fix 32bit

Merge pull request tinylib#90 from tinylib/raw-print

run goimports everywhere, in parallel; don't write intermediate code to disk