added DEBUG support
added DEBUG support

cc @gpichot you can run `HDF5_DEBUG=1 make somthing` to run in debug
mode or just `make <…>` for release

HDF-NI/hdf5.node,ryancole/hdf5.node,ryancole/hdf5.node,ryancole/hdf5.node,HDF-NI/hdf5.node,HDF-NI/hdf5.node