Add support for 72x40px SSD1306 modules

[jamwaffles]

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

• [ ] ~Check that you've added documentation to any new methods~
• [x] Rebase from master if you're not already up to date
• [x] Add or modify an example if there are changes to the public API - graphics_i2c_72x40
• [x] Add a CHANGELOG.md entry in the Unreleased section under the appropriate heading (Added, Fixed, Changed, etc)
• [x] Run rustfmt on the project with cargo fmt --all - CI will not pass without this step
• [x] Check that your branch is up to date with master and that CI is passing once the PR is opened

PR description

Adds support for the 72x40px variant of the SSD1306. I believe this is also sometimes advertised as a 70x40px display. This Reddit thread was handy in figuring out a display offset of (28, 0) pixels. This is handled by the driver, so no user code needs to change.

[jamwaffles]

Hey @therealprof looks like this fell down the back of the couch. Would you have a moment to review it? It not I think I'll merge it as-is.

[jamwaffles]

Released in 0.3.0-alpha.4.