Merge branch 'release/0.6.2' into develop
fix #15 (invalid soql building from $exists operator)
fix soql building error when operand value is empty array
add soql-builder test for $exists operator
Merge branch 'fix/id/15' into develop
change ver to 0.6.3
update change history in README.md
Merge branch 'release/0.6.3'
Merge branch 'master' into travis-ci