Run a full W3C sync (#850)

This update is the result of running a full synchronization with the W3C API
(instead of an incremental one). Since this is the first time that a full sync
is done, many entries get updated at once. The updates bring more consistencies
between the entries (for example, authors appear everywhere, instead of just in
versions), add missing versions for a number of specs, and updates the `source`
field of all entries to target the W3C API.

This last update is going to be useful to add support for specification series,
as discussed in #811 (the `source` field can then serve as identifier from a
W3C API perspective).