Fixed font for examples
Removed extraneous tag in DoxygenLayout.xml
More spacing on Doxygen version number, associated position change for seach boxes.
* Add documentation for gpio_irq_callback_t and rtc_callback_t (fixes#175)
* Hook up pico_binary_info and pico_bootsel_via_double_reset to the Doxygen index
* Add link to new Raspberry Pi Pico FAQ
* Consistently add parentheses for \sa or \see links to function-names
* Use consistent capitalisation for 'GitHub'
* Small typos and markup errors