Return number of updated rows

Closes #134
Bump clojure.java.jdbc version to 0.3.5
Delete unused functions
Reworks the transaction macro so it would optionally accept a map with options as first parameter (currenly recognizes :isolation and :read-only?)
Merge pull request #246 from ls4f/isolated-transaction

Adds a helper for transactions with a specific isolation level
Merge remote-tracking branch 'upstream/master'