Add reflection plugin.

Add reflection plugin.

The source for the easter egg example is not included, but it is:

        org 0x7c00
        ;  clear screen
        mov ah,0
        mov al,3
        int 0x10
        ; print string
        mov ah,0x13
        mov bl,0xa
        mov al,1
        mov cx,len
        mov dh,0
        mov dl,0
        mov bp,hello
        int 0x10
        hlt
hello:  db "*** Hello from nbdkit! ***",0xd,0xa
len:    equ $-hello
        ; pad to end of sector
        times 510-($-$$) db 0
        ; boot signature
        db 0x55,0xaa