Merge pull request #46 from aldenquimby/master

executeAndFetch fallback to executeScalar
fixes #37, Added a shallow layer between Slf4j and sql2o, making the slf4j dependency optional. If slf4j is not in the classpath, debug messages will be ignored and warnings will be written to System.err
added Alden Quimby to list of developers in pom.xml
make joda optional