Major changes:

• fnet: Fix compile warning in gcc-8

Major changes:

• fev: Makes fev_ APIs robuster

Major changes:

• Refine flog helper macros

Major changes:

• fev: fev_timer_service introduces interval parameter
• fev: Makes fev_timer_service repeated timer more accurate

Major changes for this release:

• flog: Set log-level per logger
• flog: Set rolling-size per logger
• flog: Set flush-interval per logger
• flog: Set logger as the background thread name
• flog: Replace gettimeofday with clock_gettime