Add DisplaySize64x32 to prelude

[williamdes]

Hi! Thank you for helping out with SSD1306 development! Please:

• Check that you've added documentation to any new methods
• Rebase from master if you're not already up to date
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PR description

I noticed that 64x32 was missing in prelude

[eldruin]

Sounds good to me, thanks.
Could you also:

• Add a CHANGELOG.md entry in the Unreleased section under the appropriate heading (Added, Fixed, Changed, etc)
• Run rustfmt on the project with cargo fmt --all - CI will not pass without this step

[williamdes]

Sounds good to me, thanks.

Thank you for the quick review, I will clone the repo and process this soon

[eldruin]

Thank you! I will add it to the changelog myself.