Makefile: replaced $(FOO) variable syntax by ${FOO}
README: Added an INSTALL section
Fix build with clang
Update README.md
lua-sysctl is now usable under FreeBSD < 9 and >= 9

  FreeBSD 9 introduced new sysctl(3) return types for 64 bits integers
  (both signed and unsigned, respectively CTLTYPE_S64 and CTLTYPE_U64)
  and removed CTLTYPE_QUAD and quad_t. It is a good move overall and we
  now test at compile time for the FreeBSD version (using
  __FreeBSD_version macro) allowing us to support both quad_t and
  int64_t / uint64_t.
Merge branch 'master' of git://github.com/kAworu/lua-sysctl