Rename the dictionary file from `multi_block_core.dic` to `cif_multi.dic`

[vaitkus]

This renaming follows the conventions discussed in COMCIFS/cif_core#488.

It would be good to adopt before making the official release of the pdCIF dictionary that imports it so that the name would not need to be changed in the future releases.

[publcif]

For info: the current file name for the 'official' release of the MULTIBLOCK_DIC is cif_core_multiblock_1.0.0.dic at https://doi.org/10.1107/cifdic_000004 which resolves to https://www.iucr.org/__data/iucr/cif/dictionaries/cif_core_multiblock_1.0.0.dic

[vaitkus]

@publcif thank you very much for noting this.

@jamesrhester , @nautolycus any suggestions of how we should proceed here? Should the cif_core_multiblock.dic name be adopted as the 'official' one instead of the previously discussed cif_multi.dic?

[jamesrhester]

I tend to favour sticking with cif_core_multiblock, to explicitly make that strong link with cif_core and multiple blocks. We can still make a "CIF multi" logo. Happy to go with whatever @nautolycus thinks, though.