docstr: Parse the AFM file in file object *fh*.
code: def __init__(self, fh):
      """Parse the AFM file in file object *fh*."""
      self._header = _parse_header(fh)
      self._metrics, self._metrics_by_name = _parse_char_metrics(fh)
      self._kern, self._composite = _parse_optional(fh)
  
imports: from collections import namedtuple
  import logging
  import re
  from ._mathtext_data import uni2type1
label_desc: Use image node_id 1 to create a new AFM object  with example: obj = AFM(fh)