Build an index for a repeat-masker alignment file by repeat-masker ID.

def index_repeatmasker_alignment_by_id(fh, out_fh, vebrose=False):
  """Build an index for a repeat-masker alignment file by repeat-masker ID."""
  def extract_UID(rm_alignment):
    return rm_alignment.meta[multipleAlignment.RM_ID_KEY]

  index = IndexedFile(fh, repeat_masker_alignment_iterator, extract_UID)
  index.write_index(out_fh)