merge
add support to int32, int, uint, uint32, uint64 for pk
bug fixed
docs improved
Merge pull request #37 from nashtsai/scrolling-rs

Scrolling rs
tests bug fixed
add benchmark tests for mssql
Merge pull request #39 from nashtsai/master

make Import() call Db.Exec() directly
add Contributing.md
merge
resolved #36
Merge branch 'master' into dev