Common typos and linting?

Common typos.

It would be nice if the parser handled these more gracefully instead of breaking a block or bailing out -- perhaps providing better feedback.

- leading semicolon before the very first entry
- parser bug? should any leading ; be ignored?
- should any two empty ; ; be ignored?)
- accidentally writing : instead of ; as a separator
- accidentally writing [ or ] instead of { or } for arguments
- 1.c2. (trailing dot!)
- 1.2c , 1.2r (reversed number and short attribute)
- 1.c (missing attribute argument)
- bad gates: ``panelcode

Checking could also be built into a linter. Optionally, the linter could be run before rendering.