documentation and cleanup.
minor refactoring (drop unused argument, change return type to more general one)
add bare-minimum test for EmbeddedCDXServerIndex.
fix ARI-3713. set regular expression on statuscode field to new baseStatusRegexp property.
revert method signature change to maintain compatibility with existing AIT wayback.
Merge pull request #16 from kngenie/ARI-3713

Add a property to EmbeddedCDXServerIndex for customizing default statuscode filter.