Add Nintendo DS ROM loader plugin

These commits add a bin plugin to load Nintendo DS ROMs.

Example:

```
r2 ../Mario\ Kart\ DS.nds 
 -- The door is everything..
[0x02000800]> S
[00] * 0x00004000 rwx va=0x02000000 sz=0xe7534 vsz=0xe7534 arm9
[01] . 0x00141600 rwx va=0x02380000 sz=0x289a4 vsz=0x289a4 arm7
[0x02000800]> ie
[Entrypoints]
vaddr=0x02000800 paddr=0x00000000 baddr=0x02000000 laddr=0x00000000
vaddr=0x02380000 paddr=0x00000000 baddr=0x02000000 laddr=0x00000000

2 entrypoints

[0x02000800]>
```

And a pic of the visual mode with another ROM (Kirby!) loaded:

![screen shot 2014-09-24 at 23 59 34](https://cloud.githubusercontent.com/assets/1909038/4396567/354b2fae-4436-11e4-985b-c02122e3dc66.png)

It will only load official Nintendo ROMs, because it does the check with the Nintendo logo, some modifications may be made in the future to also load hombrew ROMs.