clang-format: Add column layout formatting for braced lists

With this patch, braced lists (with more than 3 elements are formatted in a
column layout if possible). E.g.:

  static const uint16_t CallerSavedRegs64Bit[] = {
    X86::RAX, X86::RDX, X86::RCX, X86::RSI, X86::RDI,
    X86::R8,  X86::R9,  X86::R10, X86::R11, 0
  };

Required other changes:
- FormatTokens can now have a special role that contains extra data and can do
  special formattings. A comma separated list is currently the only
  implementation.
- Move penalty calculation entirely into ContinuationIndenter (there was a last
  piece still in UnwrappedLineFormatter).

Review: http://llvm-reviews.chandlerc.com/D1457
llvm-svn: 189018