+S4U new features:
+ - s4u::Io: IOs go asynchronous as activities. This comes with new methods in the
+ s4u::Storage class:
+ - io_init(sg_size_t, s4u::Io::OpType) to create a READ or WRITE asynchronous
+ IO operations that can be started, waited for, or canceled as a regular
+ activity.
+ - read_async(sg_size_t) and write_async(sg_size_t) which are wrappers on
+ io_init() + start()
+ - Fully reimplement auto_restart mechanism that was utterly broken
+ (fix #22, #131 and #281 that were all very related)
+ - When creating an actor from a function and its parameters,
+ move-only parameters are not allowed anymore, as it would prevent
+ the actor to be restartable if its parameters are consumed on run.
+
+Tracing:
+ - Rename 'power' and 'power_used' variables into 'speed' and 'speed_used'
+ - New host variable: 'core_count'
+
+XBT:
+ - Remove xbt_os_thread_specific features
+ - Remove portability wrapper to condition variables
+ - Remove xbt_os_thread_yield()
+