Migrate PackratParsers tests to JUnit.

Most of the migration is straightforward. One exception is packrat3
(migrated to `test3` method). I simplified returned result by getting
rid of useless Unit by changing this rule:

  repMany1(a,b) ~ not(b)

into this rule:

  repMany1(a,b) <~ not(b)

Also, I made all rules to be type safe.

When constructing expected results, I decided to use scala.Symbol that
allows us to use a bit more concise syntax for construction of one
character strings. See `threeLists` method for details.
Migrate RegexParsers tests to JUnit.
Migrate JavakTokenParsers tests to JUnit.