Add ANTIOCH_VERSION_AT_LEAST(major, minor, micro)

Following http://gcc.gnu.org/onlinedocs/cpp/Common-Predefined-Macros.html
this macro is usable in situations like
 #if ANTIOCH_VERSION_AT_LEAST(0, 0, 4)
   // Use post 0.0.4 APIs
 #else
   // Use pre 0.0.4 APIs
 #endif
and beats the common
 #define GCC_VERSION (  __GNUC__ * 10000     \
                      + __GNUC_MINOR__ * 100 \
                      + __GNUC_PATCHLEVEL__)
approach since it doesn't require break working with values like 30200.
Merge pull request #17 from RhysU/ANTIOCH_VERSION

Add ANTIOCH_VERSION_AT_LEAST(major, minor, micro)