libuEv v1.2.1

Minor fix release.

Changes

• Private data members in uev.h have now been moved to a new file
  called private.h. This will hopefully make it easier to understand
  what a user of libuEv is allowed to play around with. Thanks to @vonj
  for the discussions around this!
• All builds of libuEv now default to use -fPIC, this bloats the code
  slightly, but ensures that linking works for all use cases, withouth
  introducing unnecessary complexity.

Fixes

• Fix install/uninstall Makefile recipes so they work for both static
  and dynamic builds. Also, make sure to install all required headers.
• Jakob Eriksson noticed that O_CLOEXEC does not exist in the Debian 6
  EGLIBC, but EPOLL_CLOEXEC does, and is also what epoll_create1()
  should use. Thank you @vonj!