Merge src/unix/timer.c and src/win/timer.c into src/timer.c. This
changes the Windows implementation from a binary tree to a binary
heap for generally better performance.
PR-URL: https://github.com/libuv/libuv/pull/1882
Reviewed-By: Bartosz Sosnowski <bartosz@janeasystems.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
