Fix csv metrics documentation. Directory creation

When the Metric's CSV reporter is enabled, it doesn't write to a file, but
instead writes a series of files to a specified directory. This commit fixes
all references of the single file notion.

This commit also creates the CSV reporter directory if it doesn't already
exist on start up. An appropriate test was created to confirm behavior.
added documentation for tasks [ci skip]
Update Liquibase XSD in dropwizard-example
Fix output of data in DbDumpCommand, fixes #476
Merge pull request #596 from spagalloco/tasks-documentation

added documentation for tasks
Make the classloader used in DiscoverableSubtypeResolver more easily changeable.
Create parent directories and fail fast
Appease FindBugs with mkdirs return value
Merge pull request #597 from reines/extendable_classloader

Make the classloader used in DiscoverableSubtypeResolver more easily changeable
Merge pull request #592 from joschi/476-db-dump-ignores-data

Fix output of data in DbDumpCommand
Merge pull request #583 from nickbabcock/csv-fix

Fix csv metrics documentation. Directory creation