Convert timestamp type.
Expire log.
Add scalastyle.
Fix style. Add a license notification.

warning file=/home/sloan/workspace/logback-mongodb-appender/src/main/scala/logback/mongodb/MongoDBAppender.scala message=Header does not match expected text line=1
Fix style. Remove magic number.

warning file=/home/sloan/workspace/logback-mongodb-appender/src/main/scala/logback/mongodb/MongoDBAppender.scala message=Magic Number line=62 column=27
warning file=/home/sloan/workspace/logback-mongodb-appender/src/main/scala/logback/mongodb/MongoDBAppender.scala message=Magic Number line=125 column=32
Do not use ImportGroupingChecker.

I don't like grouping import.
Fix style. Remove repeated string literal.

warning file=/home/sloan/workspace/logback-mongodb-appender/src/main/scala/logback/mongodb/MongoDBAppender.scala message=The string literal "timestamp" appears 4 times in the file. line=103 column=33