Refactor to use modern timerfd and epoll

This is a major refactor of the original design by Flemming Madsen.  It
converts the library timers from poll() to timerfd, which at the same
time also unifies the file and timer watchers into one design.  The idea
is to also add signalfd to the mix later on.

Also a couple of hundred kilobytes smaller, although size a secondary
goal.  The primary goal is to further simplify the internal design and
to continuously strive to employ modern APIs.

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

Makefile

@@ -27,7 +27,7 @@
 CC          = $(CROSS_COMPILE)gcc
 AR          = $(CROSS_COMPILE)ar
 STRIP       = $(CROSS_COMPILE)strip
-CFLAGS     += -fPIC -g -Os
+CFLAGS     += -fPIC -Os
 CPPFLAGS   += -W -Wall -Iinclude
 ARFLAGS     = crus
 JUNK        = *~ *.bak *.map .*.d DEADJOE *.gdb *.elf core core.*