allow multiple statements in inserts

[jnc-nj]

ref #38
I agree with the author this should be part of the default set of behaviours.
Seeing as the issue was opened in '16 (and I needed the functionality) I made my own edits.
The implementation is admittedly hacked together though, but works:

(insert-into :person (set= :sex "male" "female" "god" :name "fred" "tom" "jesus"))
#<SXQL-STATEMENT: INSERT INTO person (name, sex) VALUES ('jesus', 'god'),('tom', 'female'),('fred', 'male')>