Improve wake up performance when reading a book

[cgreening]

We "dehydrate" the state of the epub list so that when we come back from deep sleep it's quite fast to update.

When reading a book we need to redo the parsing and layout of the current section. Can we persist the state of reading as well?

[martinberlin]

+1 up-vote for this one since will improve a lot the usability experience.
Maybe you can create some: high, medium, low (priority labels) so we can vote what will be the ones to focus on first.

From time to time it happens that it hangs on wake up leaving the hourglass on, no further interaction possible except a hard reset. Sadly it never happened so far when I’m debugging via usb so I cannot copy the Serial feedback.