This changes the LOG macro to be varadic removing the need for all
callsites to have double bracketing and allows for future improvement
on how we use the logging macros.
The callsites were changed with coccinelle and the changes checked by
hand. Compile tested for several frontends but not all.
A formatting annotation has also been added which allows the compiler
to check the parameters and types passed to the logging.
The core no longer needs to run the event polling loop as fetches are now
scheduler driven. This is part of a series which will ultimately remove
netsurf_poll callback altogether.
