Export formats

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As part of KBase's work with ontologies in semsql, it would be very handy to be able to export as DSV directly, rather than going via the sqlite database.

We could put together a file similar to `build.Makefile` to perform the conversions, but I am wary of changes being made in the semsql sqlite build process that we'd have to ensure that we kept up with. I was therefore wondering about adapting the current build command to export either DSV or sqlite, depending on what args it is given.

[build.Makefile](src/semsql/builder/build.Makefile) line 51 onwards:
```
# -- MAIN TARGET --
# A db is constructed from
# (1) triples loaded using rdftab
# (2) A relation-graph TSV
%.db: %.owl %-$(RGSUFFIX).tsv $(PREFIX_CSV_PATH)
rm -f $@.tmp && \
cat $(THIS_DIR)/sql_schema/semsql.sql | sqlite3 $@.tmp && \
echo .exit | sqlite3 -echo $@.tmp -cmd ".mode csv" -cmd ".import $(PREFIX_CSV_PATH) prefix" && \
rdftab $@.tmp < $< && \
sqlite3 $@.tmp -cmd '.separator "\t"' ".import $*-$(RGSUFFIX).tsv entailed_edge" && \
gzip -f $*-$(RGSUFFIX).tsv && \
cat $(THIS_DIR)/indexes/*.sql | sqlite3 $@.tmp && \
echo "ALTER TABLE statements ADD COLUMN graph TEXT;" | sqlite3 $@.tmp && \
(test -d views && find views -maxdepth 1 -name '$(notdir $*)*.sql' -type f -print0 | xargs -0 -I{} sh -c 'sqlite3 $@.tmp< "$$1"' sh {} || echo no views ) && \
mv $@.tmp $@
.PRECIOUS: %.db
```
Alter this so that if the desired output is DSV, the rdftab command is run but the sqlite db loading is omitted. Relevant files, including prefixes, relation graph, and schema SQL could be moved to a directory together or something like that.

Inizia da src/semsql/builder/build.Makefile, in particolare dal target principale intorno alla riga 51, e segui come rdftab, il relation-graph TSV, prefixes e sql_schema/semsql.sql alimentano la build di SQLite. Definisci come il comando di build seleziona l'output DSV rispetto a quello SQLite, quindi verifica che l'output DSV ometta il caricamento di SQLite mentre la build del database esistente rimane intatta.

Scritto dal modello di indicizzazione a partire dal testo della issue.