Now callback functions get the URI of the request, this allows to use a
single resource for multiple different URIs.
The is_json flag is now gone for the to-string function, instead the
macro has an is_str flag. If set this automagically produces quotes
around the string for json output.
Now from-string functions can return an error-code, 0 for success, -1
for error.
Otherwise a crash results with a bootloader compiled with a newer AVR
toolchain (e.g. Debian Jessie). If you still have an ages-old bootloader
without a jump-table, as a short-term measure you can revert this change
in your run.sh. As a long-term fix we recommend you get your bootloader
updated!
