Use file size in bytes, which is less error-prone and conforms to DCAT

Following up on comment in #32 to which @mhogeweg agreed

>Please just state the filesize in bytes. The tiny difference in the JSON file's size between having values like "1000000000" versus "1GB" isn't worth the extremely high likelihood that people will get confused between GB and GiB, etc. Also, it's much easier for an implementer to get a filesize in bytes than it is to transform that filesize to the appropriate abbreviated form.