add core package
to 2-variables query
rename listSubject => listXPO
add .gitkeep
QueryTarget#list** returns TripleIter
rename XXXQuery -> XXX
implements all PrimitiveQuery
implements QueryParser
implement Triples
fix Resource#equals

for faster execution
implement RDFFileReader
implement (complex) query
implement rule
implement multiple rules
add SAT solver example
Merge branch 'develop'