feature: allow blank lines in enumConstant lists

[clementdessoude]

Fix #259

What changed with this PR:

• blank lines are not completely removed in enumConstant lists: we allow one blank line between two enum constants

Example

// Input
public enum OtherEnum {
  ONE, TWO,

  THREE,



  FOUR,
  /* Five */
  FIVE,

  /* Six */
  SIX


}

// Output
public enum OtherEnum {
  ONE, 
  TWO,

  THREE,

  FOUR,
  /* Five */
  FIVE,

  /* Six */
  SIX
}