Add mdl loader

[yuripourre]

http://tfc.duke.free.fr/coding/mdl-specs-en.html

    char: 1 byte
    short: 2 bytes
    int: 4 bytes
    float: 4 bytes
    ubyte: 1 unsigned byte

/* MDL header */
struct mdl_header_t
{
  int ident;            /* magic number: "IDPO" */
  int version;          /* version: 6 */

  vec3_t scale;         /* scale factor */
  vec3_t translate;     /* translation vector */
  float boundingradius;
  vec3_t eyeposition;   /* eyes' position */

  int num_skins;        /* number of textures */
  int skinwidth;        /* texture width */
  int skinheight;       /* texture height */

  int num_verts;        /* number of vertices */
  int num_tris;         /* number of triangles */
  int num_frames;       /* number of frames */

  int synctype;         /* 0 = synchron, 1 = random */
  int flags;            /* state flag */
  float size;
};