Usage
    http://skmatic.x3dna.org/api [options] url=|model@
    http://skmatic.x3dna.org/api/pdb/pdb_id  -- for a pre-calculated PDB entry
    http://skmatic.x3dna.org/api/help        -- display this help message
Options
    block_file=styles-in-free-text-format [e.g., block_file=wc-minor]
    block_color=nt-selection-and-color    [e.g., block_color='A:pink']
    block_depth=thickness-of-base-block   [e.g., block_depth=1.2]
    r3d_file=true-or-FALSE(default)       [e.g., r3d_file=true]
    raw_xyz=true-or-FALSE(default)        [e.g., raw_xyz=true]
Required parameter
    url=URL-to-coordinate-file [e.g., url=https://files.rcsb.org/download/1ehz.pdb.gz]
    model@coordinate-file      [e.g., model@1ehz.cif]
    # Only one must be specified. 'url' precedes 'model' when both are specified.
    # The coordinate file must be in PDB or PDBx/mmCIF format, optionally gzipped.
Examples
    http -f http://skmatic.x3dna.org/api block_file='wc-minor' model@1ehz.cif r3d_file=t
    http -f http://skmatic.x3dna.org/api url=https://files.rcsb.org/download/1ehz.pdb.gz -d -o 1ehz.png
    http http://skmatic.x3dna.org/api/pdb/1ehz -d -o 1ehz.png
    # with 'curl'
    curl http://skmatic.x3dna.org/api -F 'model=@1msy.pdb' -F 'block_file=wc-minor' -F 'r3d_file=1'
    curl http://skmatic.x3dna.org/api -F 'url=https://files.rcsb.org/download/1ehz.pdb.gz' -o 1ehz.png
    curl http://skmatic.x3dna.org/api/pdb/1ehz -o 1ehz.png