Fix omnivore metadata file strings

[robmcmullen]

With the conversion to use future in atrcopy, the .omnivore file contains things like:

    "segment parser": {
        "py/object": "atrcopy.parsers.XexSegmentParser",
        "py/state": {"segments": [{"py/object": "atrcopy.ataridos.XexContainerSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [0, 24588], "can_resize": true, "error": null, "map_width": 40, "memory_map": [], "name": "XEX (Atari 8-bit executable)", "page_size": -1, "start_addr": 0, "uuid": {"py/newargs": {"py/tuple": ["efc94071-e39d-40a1-bc27-899fb5ea9027"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}}, {"py/object": "atrcopy.segments.ObjSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [6, 8], "can_resize": false, "data_start": 6, "error": null, "map_width": 40, "memory_map": [], "metadata_start": 2, "name": "", "page_size": -1, "start_addr": 736, "uuid": {"py/newargs": {"py/tuple": ["8988287b-1873-4075-8b79-3e2302e38ef3"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}}, {"py/object": "atrcopy.segments.ObjSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [12, 88], "can_resize": false, "data_start": 12, "error": null, "map_width": 40, "memory_map": [], "metadata_start": 8, "name": "", "page_size": -1, "start_addr": 14722, "uuid": {"py/newargs": {"py/tuple": ["a200ef0e-66d8-4b5e-a6a3-c7b610f76543"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}}, {"py/object": "atrcopy.segments.ObjSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [92, 24588], "can_resize": false, "data_start": 92, "error": null, "map_width": 40, "memory_map": [], "metadata_start": 88, "name": "", "page_size": -1, "start_addr": 16384, "uuid": {"py/newargs": {"py/tuple": ["93527854-ac61-4b0b-b0f9-120197c98ad5"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}}], "strict": true}
    }, 
    "serialized user segments": [
        {"py/object": "omnivore8bit.utils.segmentutil.AnticFontSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [16476, 17500], "can_resize": false, "error": null, "map_width": 40, "memory_map": [], "name": "Playfield font", "page_size": -1, "start_addr": 32768, "uuid": {"py/newargs": {"py/tuple": ["f8286971-48cc-4274-a2ff-d08bda65dc2a"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}},
        {"py/object": "atrcopy.segments.DefaultSegment", "py/state": {"_order_list": null, "_rawdata_bounds": [92, 16476], "can_resize": false, "error": null, "map_width": 256, "memory_map": [], "name": "Playfield map", "page_size": -1, "start_addr": 16384, "uuid": {"py/newargs": {"py/tuple": ["eb6acdab-a981-48ba-bcd9-96222ed9d47a"]}, "py/object": "future.types.newstr.newstr"}, "verbose_name": null}}