Add license and project url to project.clj
Ignore all .lein-* files
Initial transaction support
Introduce a way to explicitly start a transaction

Only necessary if transaction operations will occur in multiple
threads. See https://github.com/thinkaurelius/titan/wiki/Multi-Threaded-Transactions
for more info.
Support 0.13.0
Avoid clojure.core symbol shadowing
More test coverage for basic transactions
Naming
Catch Throwables
Add concurrent tx test