Changes for version 0.13
- add HUSH_VMSISH
- add -DPERL_OP_PARENT support, replace MORESIB and LASTSIB by SIBLING. SIBLING appears now in <5.22 perl ops also as flag, even if it's a pointer, to be consistent with 5.22.
- protect against B::NULL
- add README, release and test_cover make targets
- B::Flags - Friendlier flags for B