The package with the main function should always have the name main.
This was not the case in three packages.
This was silently allowed before, but since a TinyGo change
(https://github.com/tinygo-org/tinygo/pull/1592) this now results in a
linker failure.
Perhaps this should result in a better error message in TinyGo. However,
the example code also needs to be fixed, so hence this PR.