implemented composite key
Merge branch 'master' into compositekey
add benchmark tests
merge composite key
Merge pull request #33 from nashtsai/compositekey

Compositekey
refactoring db interface
Merge branch 'master' of github.com:lunny/xorm

# Please enter a commit message to explain why this merge is necessary,
# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.
use 4 spaces replace tab
use tabs
tidy up comments
resolved merger from upstream
code tidy up