Returns link to `ft` in source code.

def get_function_source(ft, **kwargs)->str:
    "Returns link to `ft` in source code."
    try: line = inspect.getsourcelines(ft)[1]
    except Exception: return ''
    mod_path = get_module_name(ft).replace('.', '/') + '.py'
    return get_source_link(mod_path, line, **kwargs)