expand_braces(), str_expand_braces(), and glob() now support a new argument engine (#4):

• If 'r' use a pure R parser.
• If 'v8' use the 'braces' Javascript parser via the suggested V8 package.
• If NULL use 'v8' if 'V8' package detected else use 'r';
  in either case send a message() about the choice
  unless getOption(bracer.engine.inform') is FALSE.

The 'braces' Javascript parser can handle some edge cases that the pure R parser cannot.