Match messages to JS[LH]int where appropriate, and ensure consistent message formatting (closes #163)

This pull request updates ESLint warning messages so that they match their JS[LH]int counterparts where appropriate. It uses the messages from the most recent versions of JS[LH]int.

It also ensures that all existing messages follow a consistent format, ending with a period (many messages already did this, but not all).

Finally, it renames the "too-many-params" test file to "max-params", which matches the name of the rule and therefore follows the apparent convention.