remaining warnings

[chrishavlin]

#100 fixes a few, but there are some that are coming from yt_idv (not its dependencies) that I wasn't sure what to do with.

This one should be easy, but I'm confused by traitlets :)

yt_idv/tests/test_yt_idv.py::test_snapshots
  /home/chavlin/src/yt_general/yt_idv/yt_idv/scene_components/blocks.py:30: DeprecationWarning: metadata {'trait': <traitlets.traitlets.CFloat object at 0x7f2add86ad30>} was set from the constructor. With traitlets 4.1, metadata should be set using the .tag() method, e.g., Int().tag(key1='value1', key2='value2')
    slice_position = traitlets.Tuple((0.5, 0.5, 0.5), trait=traitlets.CFloat())

And then a bunch related to missing characters, e.g.,

yt_idv/tests/test_yt_idv.py::test_annotate_text
  /home/chavlin/src/yt_general/yt_idv/yt_idv/scene_data/text_characters.py:36: UserWarning: Glyph 9 (	) missing from current font.
    self.font.set_text(chr(char_code), flags=LOAD_FORCE_AUTOHINT)

[chrishavlin]

(there are a couple others coming from dependencies, but since we don't have pytest set to fail on warnings it's not worth catching them in pytest at present...)