Docs: new documentation and warnings cleanup
This change set
- adds a high-level description of application startup flow. Some parts are missing, but hopefully we can use this description as a base to expand on.
- adds a few notes about memory regions and their use in ESP-IDF.
- add SPI flash and partition APIs page
- fixes all Doxygen warnings in header files
- enables build failures on new Doxygen warnings
See merge request !201
This commit fixes several issues with state handling in nvs::Page. It also adds extra consistency checks in nvs::PageManger initialization.
These changes were verified with a new long-running test ("test recovery from sudden poweroff"). This test works by repeatedly performing same pseudorandom sequence of calls to nvs_ APIs. Each time it repeats the sequence, it introduces a failure into one of flash operations (write or erase). So if one iteration of this test needs, say, 25000 flash operations, then this test will run 25000 iterations, each time introducing the failure point at different location.
