Renamed cpptempl internal classes.

- Renamed Token* classes and types to Node*.
- Removed "Statement" from StatementToken classes and types.
- This simplifies the names and reduces confusion caused by having
  two sets of "tokens".
- Changed some type names to match existing code style by removing
  "_t" suffix. Also changed [stmt_]token_type_t enum to TokenType.

Signed-off-by: Chris Reed <flit@me.com>