Add the option for using blosc filter

[LauZanMo]

See #978

This PR adds a custom blosc filter and has been tested in create_dataset_double.cpp in examples folder.

[alkino]

We will have to fix that.

[LauZanMo]

Since blosc is an extra plugin of hdf5, it is necessary to compile and link this external libraries. hdf5-blosc can not be found using find_package macro since it is packaged too simple here. I haven't figured out an elegant way to link this library.

[alkino]

What I mean is that hard coded path to your system is not the valid way to give access to blosc.

[alkino]

@1uc I don't think this is how you think how your wrapper, right?
We will need to put this helper in an other place?

[LauZanMo]

Unlike szip, a built-in filter in hdf5, blosc filter must be registered before use. Perhaps a register wrapper should be added here.

[1uc]

Here I'd prefer splitting it differently:

inline herr_t h5p_set_filter(....) {
    herr_t err = H5Pset_filter(...);
    if (err < 0) {
        HDF5ErrMapper::ToException<PropertyException>("Error setting setting filter.");
    }
    return err;
}

Then in Blosc we do the other half:

inline void Blosc::apply(const hid_t hid) const {
    char *version, *date;
    if (register_blosc(&version, &date) < 0) {
        HDF5ErrMapper::ToException<PropertyException>("Blosc filter unavailable.");
    }
    detail::h5p_set_filter(plist_id, FILTER_BLOSC, H5Z_FLAG_OPTIONAL, 7, cd_values);
}

If you want the error message to contain the word "blosc" when set_filter fail, one would need to catch and rethrow with a different error message.

[1uc]

To avoid the issue with forcing an optional dependency (blosc) on all users, we'll need to rework the PR. I think we can safely move all blocs related code to highfive/blosc.hpp. Ensure we include the header for blosc. The wrapper for H5Pset_filter stays in h5p_wrapper.hpp.

To fix the build-system maybe the following works:

1. Temporarily remove all CMake code.
2. For testing only add it back similar to how boost and Eigen are handled.
3. Setup CI that installs blosc and runs the tests.

This has the advantage (for us) that we don't specify how to find/link to blosc, it's left up to the user. This is different everywhere and we're likely to get it wrong if blosc doesn't have *-config.cmake files. The solution @LauZanMo shows presumably works very well for their usecase, but unfortunately for a library that's not suitable. We can always add a target highfive::blosc if needed, but we can't take it away.

[1uc]

These are both leaked, because register_blosc uses strdup which requires us to call free.

[1uc]

This function likely can't be called twice. Therefore, if two property lists with Blosc are created I suspect a misleading error message will be printed. It's unclear if it'll work, because register_blosc seems to unconditionally return 1; (despite defining and setting a retval).