Major refactor: API change, code cleanup, remove calloc()/free()

- Rename all _create() functions --> _init()
- Rename all _delete() functions --> _stop()
- Watchers are automatically started, except
- Timer watchers are automatically started by uev_run()
- Allow I/O watchers to watch either EV_READ/EV_WRITE or both events
- Extend callbacks with a received events field
- Remove calloc()/free(), let user handle this
- Make event has-a context when initializing it => simplifies API
- Internal uev_watcher_*() API mostly handles epoll stop/start

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

Makefile

@@ -34,7 +34,7 @@ CC          = $(CROSS)gcc
 AR          = $(CROSS)ar
 STRIP       = $(CROSS)strip
 CFLAGS     += -fPIC -Os
-CPPFLAGS   += -W -Wall -Iinclude
+CPPFLAGS   += -W -Wall -Werror -Iinclude
 ARFLAGS     = crus
 JUNK        = *~ *.bak *.map .*.d DEADJOE *.gdb *.elf core core.*