samemapper support
Merge pull request #50 from nashtsai/dev

caching session bounded sql.Stmt to increase performance
merge
improved docs
improved tests
move test files to tests/ subdir
move tests to tests subdir & refactoring
bug fixed
doc & version
add struct, slice, map scan for db
performance improved for db.ScanStruct2
improved benchmark test for db.go
add Row, Stmt etc. for db.go
add querymap & querystruct for tx
a little performance improved
move types to core subdir
use core.DB instead of sql.DB
add map & struct methods for core.Stmt