Add abortion handler to Nested Protothreads.
Update unittests (passed).

A NPT task can now be aborted using an abortion context,
which will also recursively abort all nested tasks.
You can specify code to cleanup internal states,
for when an abortion context is received.
Typos.
Remove deprecated `preserveTag()` from I2cTagAdapter.
SSD1306 does not need a WriteReadAdapter.