* facefile format

This file preserves subject head information.
File accessor is stored $POSITIONING/file_accessor/facefile
Format is below.

header
    .file_type : file type    [string] = ('FACE-MAT')
    .version   : file version [double]
subject
    .name      : subject name  [string]
    .birth     : subject birth [string]
    .mri_file  : mri file location in the database.

mri_hdr_key    : MD5 hash key made from analyze header file(*.hdr) [string]
mri_key        : MD5 hash key made from analyze image  file(*.img) [string]

coord_type     : coordinate system of landmark position, spherical center, 
                 surf_face, marker_on_mri. [string] (='SPM_Right_m')
landmark
    .lpa       : Left  preauricular [1x3 double]
    .rpa       : Right preauricular [1x3 double]
    .nasion    : Nasion             [1x3 double]
    .other
        .name  : Other points name list  [Nx1 cell]
        .pos   : Other points positions  [Nx3 double]

spherical_head
    .Vcenter   : center of the sphere model [1x3 double]
    .Vradius   : radius of the sphere model [1x1 double]

surf_face
    .V         : face vertex coodinate [Nx3 double]
    .F         : face patch index      [Nx3 double]
    .V_reduce  : reduced face vertex coordinate [Nx3 double]
    .F_reduce  : reduced patch index            [Nx3 double]
    .face_parm : parameter which is used for face extraction.

marker_on_mri  : marker positions on MRI
    .name      : marker name      [Nx1 cell]
    .pos       : marker positions [Nx3 double]
