support composite keys in each migration strategy ie override create table and insert statements
code cleanup
db2: use syscat.references to get reftable; have to trim the pk_colname
else will not match the column name argument;ignore primary keys when
looking at constraints (like mysql)
postgres: need to specify the current schema and database otherwise will
pick up similarly named constraints/columns etc
add sqlite support: add tests for composite keys in Test1
update readme to include sqlite