Minor enhancements
ReliableChannel stores sender references

- closes #50
Reset restart counter on successful delivery
Add missing withRestartMax to ReliableChannelProps
Event sourcing and reliable request-reply
Order processing example with reliable request-reply
Use sbt 0.12.2
Minor user guide edits
Link to service integration article
Upgrade links to Akka 2.1.0
Fix typo: etxension -> extension
add build.sbt for simplify usage in multi-modules sbt project
fix compiler warnings. refactor sbt project settings: remove duplicates
remove unnecessary return type declaration : Unit = { ... }
Use vals for Scala and Akka version
Merge pull request #56 from stig/patch-1

Fix typo in README: etxension -> extension
Improve internal reliable channel protocol