Coding style: move a static function to anonymous namespace
Add T_RAW_DWARF, T_RAW_CU

- These are for low-level, uninterpreted access to Dwarf tree.
  T_RAW_DIE and others are yet to come.

- Words (raw) and (cooked) were introduced to flip values between raw
  and cooked variants.

- Calling (unit) on T_RAW_DWARF yields T_RAW_CU's, and all of them.
  (unit) on T_DWARF yields T_CU's, but skips partial units.
  Eventually it should do transparent partial unit inlining.