Syntax updates, misc fixes, new snippets, custom status bar text

• Custom status bar text #355
• Add dbg, debug, trace, info snippet #360
• On-save check: only call cargo metadata once #365
• Syntax:
  • literal macro fragment matcher #367
  • abort on invalid struct #369
  • const functions #361
  • fix break and continue #364
  • fix lifetime on self param #366