Generate UnmarshalJSON to handle emptyStringInt types

This commit changes the code generator to generate a `UnmarshalJSON` for each
struct, so that if unmarshalled it properly handles UniFis varying integer values
via the `emptyStringInt` type.

Structs not including a field of `int` type will still have the function generated,
but it will effectively do nothing.

Fixes #18

unifi/wlan.go

@@ -2,28 +2,8 @@ package unifi
 
 import (
 	"context"
-	"encoding/json"
 )
 
-func (n *WLAN) UnmarshalJSON(b []byte) error {
-	type Alias WLAN
-	aux := &struct {
-		VLAN emptyStringInt `json:"vlan"`
-		*Alias
-	}{
-		Alias: (*Alias)(n),
-	}
-
-	err := json.Unmarshal(b, &aux)
-	if err != nil {
-		return err
-	}
-
-	n.VLAN = int(aux.VLAN)
-
-	return nil
-}
-
 func (c *Client) CreateWLAN(ctx context.Context, site string, d *WLAN) (*WLAN, error) {
 	if d.Schedule == nil {
 		d.Schedule = []string{}