Add keyword arg to select font to miniscreen display text methods

[angusjfw]

My use case is to display emojis for a memory game.

It's unfortunate that Pillow ImageFont does not support combining fonts, so that fallback fonts could be automatically used for characters not in the default. One possibility would be for us to create and use font with the combinations manually. This font option would allow a user to do so themselves at least.

[codecov]

Codecov Report

Merging #391 (0cb5c72) into master (5a7269f) will decrease coverage by 0.06%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master     #391      +/-   ##
==========================================
- Coverage   54.58%   54.51%   -0.07%     
==========================================
  Files          80       80              
  Lines        3261     3265       +4     
==========================================
  Hits         1780     1780              
- Misses       1481     1485       +4     

Flag	Coverage Δ
unittests	54.51% <33.33%> (-0.07%)	⬇️

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Impacted Files	Coverage Δ
pitop/miniscreen/oled/oled.py	32.93% <33.33%> (-0.54%)	⬇️

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