Removing 3.0.0 compatibility.

[kattni]

Fixes #9

Requires testing of bdf.py file.

[FoamyGuy]

I get this error:

Traceback (most recent call last):
  File "code.py", line 10, in <module>
  File "/lib/adafruit_bitmap_font/bitmap_font.py", line 56, in load_font
  File "/lib/adafruit_bitmap_font/bdf.py", line 43, in <module>
ImportError: cannot import name Glyph

Running on PyPortal with 5.0.0 and 5.1.0.rc0.

I will test a few other devices.

[FoamyGuy]

Same results with EdgeBadge and CPB+Gizmo 5.0.0 on both. Can recreate with REPL:

Adafruit CircuitPython 5.0.0 on 2020-03-02; Adafruit Circuit Playground Bluefruit with nRF52840
>>> from displayio import Glyph
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: cannot import name Glyph

[kattni]

@FoamyGuy I may have done this wrong then. I'll take a look tomorrow.

[tannewt]

Glyph moved from displayio to fontio so the reverse should work.

[FoamyGuy]

I was not sure how to fix the docs conf on this PR so I've created #21 to resolve it. Let me know if I should do something different.

Tested this changes successfully with the adafruit_display_text simpletest on PyPortal and PyGamer.

[kattni]

Closing in favor of #21