Returns a headerfields object (dict) which contains information on
    fields of the header, including optional pool names

def generate_headerfields(headertypes, allfield_defs, poolnames, db=False, genecentric=False):
    """Returns a headerfields object (dict) which contains information on
    fields of the header, including optional pool names"""
    hfields = {}
    for fieldtype in headertypes:
        if fieldtype == 'isoquant':
            continue
        elif fieldtype == 'proteindata':
            hfield_definitions = allfield_defs[fieldtype](poolnames, genecentric)
        else:
            hfield_definitions = allfield_defs[fieldtype](poolnames)
        hfields[fieldtype] = OrderedDict()
        for fieldname, poolnames in hfield_definitions.items():
            hfields[fieldtype][fieldname] = get_header_field(fieldname,
                                                             poolnames)
    if 'isoquant' in headertypes:
        hfield_definitions = allfield_defs['isoquant'](db, poolnames)
        hfields['isoquant'] = OrderedDict()
        for poolname in poolnames:
            for fieldname in hfield_definitions:
                hfields['isoquant'][fieldname] = get_header_field(
                    fieldname, poolnames)
    return hfields