Add little comments to examples.
Fix around placeholders with direct style join and update examples.
Update document of projection operators.
Add document of TH functions for relational-join.
Update session to call rollback before disconnect using nested bracket.
Add document of functions to query IBM DB2 system catalogs.
Update compile error message.
Add document of system catalog queries.
Add document of schema driver interface via HDBC.
Rename local variable.
Merge pull request.
Update readme.
Renamed.

--HG--
rename : relational-join-HDBC-pgTest/sample/1/Group.hs => relational-join-HDBC-pgTest/example/1/Group.hs
rename : relational-join-HDBC-pgTest/sample/1/Membership.hs => relational-join-HDBC-pgTest/example/1/Membership.hs
rename : relational-join-HDBC-pgTest/sample/1/README => relational-join-HDBC-pgTest/example/1/README
rename : relational-join-HDBC-pgTest/sample/1/User.hs => relational-join-HDBC-pgTest/example/1/User.hs
rename : relational-join-HDBC-pgTest/sample/1/create.sh => relational-join-HDBC-pgTest/example/1/create.sh
rename : relational-join-HDBC-pgTest/sample/1/drop.sh => relational-join-HDBC-pgTest/example/1/drop.sh
rename : relational-join-HDBC-pgTest/sample/1/querySample.hs => relational-join-HDBC-pgTest/example/1/querySample.hs
removing unnecesary scripts.