Use HDF5 memory management functions

[aparamon]

Currently, external buffers are allocated via malloc()

HDF5-External-Filter-Plugins/LZ4/src/H5Zlz4.c

Line 76 in d35e763

if (NULL==(outBuf = malloc(origSize)))

HDF5-External-Filter-Plugins/LZ4/src/H5Zlz4.c

Line 150 in d35e763

if (NULL==(outBuf = malloc(LZ4_COMPRESSBOUND(nbytes)

and released by free()

HDF5-External-Filter-Plugins/LZ4/src/H5Zlz4.c

Line 115 in d35e763

free(*buf);

HDF5-External-Filter-Plugins/LZ4/src/H5Zlz4.c

Line 198 in d35e763

free(*buf);

It is sub-optimal though as this method requires the plugin to be compiled with the same memory manager as HDF5 library, which is sometimes non-trivial to achieve, esp. on Windows.

HDF5 memory management functions
https://support.hdfgroup.org/HDF5/doc/RM/RM_H5.html#Library-AllocateMemory
https://support.hdfgroup.org/HDF5/doc/RM/RM_H5.html#Library-FreeMemory
should be used instead.

[zjttoefs]

That sounds like a very fair point and I also learned something. Thanks.
Would you maybe do a pull request after you've confirmed it works?
Change looks simple, but I've got little time for proper testing at the moment.