Our old stale copy of the FTS3/4 module is now deleted, replaced by
a shinier FTS5 embedded module. If at configure time we detect that
SQLite doesn't offer the FTS5 module, we will load our own, just as
we used to do with FTS4.

FTS5 brings a few differences in the ways it's meant to be extended,
the tokenizer has been updated to cope with the differences. Also,
FTS5 offers no offsets() builtin function, nor matchinfo() which we
used to implement ranking. It offers though ways to implement
additional functions, and builtin rank support which can be tweaked
to achieve the same functional results than we did.

Other than that, the ways to interact with the FTS virtual table
are roughly similar to those in FTS4, insertions and deletions have
been updated to do things the FTS5 way.

Since it's not worth to bump the database format (data is reproducted
from the journal, so we drop some embedded data such as
nie:plainTextContent), the nco:hobby property has been modified to
no longer be fulltext...