Make conf.bins work for cross compiled deps as well as the host.

Host's mrbc file should be used when cross-compiling mrbtest.c

Added conf.bins for defining bulding binaries

Added s flag to ar command

Strict runtime error checking

Remove redundant null checks.

Add check for using cdump with DISABLE_STDIO option.

Export Array#clear in array.h

Added gem :github option

Compact flags for GC

Add test cases for GC API

Skip sweeping old slots which don't contain any young object in the minor GC

Remove debug macros from mruby.h

vm.c: Enable DEBUG(x) if VM_DEBUG is defined.

improve mrbgems

Can access to current gem's name through GEMNAME from test.

Can change assert library each mrbgems. used spec.test_preload on mrbgem.rake.

assert library should set $ok_test, $ko_test, $kill_test, $asserts.

Generational Garbage Collection for mruby

Modify NODE_IF handling.

Removed XCode build