Timing and Counting methods should report warnings when necessary

[domfarolino]

Right now console.time() mentions an optionally-reported warning on trying to start an already-existing timer. We should strengthen this by implementing some sort of formal error-reporting method (#57) and making the warning mandatory.

Furthermore, console.timeEnd() in all implementations (can't remember Edge's behavior though) prints a warning when trying to end a non-existent timer. To bring the spec closer to implementations, and also align timeEnd() with countReset (currently being specced), I propose make timeEnd() also report an warning under the previously-mentioned conditions.

Edit

In short:

• time() should report a warning
• timeEnd() should:
  • remove a timer from the timer table when dealing with existing timers
  • report a mandatory error when a timer doesn't exist
• timeLog()should report a warning.
• countReset() should report a warning (it does, but we should do it formally)
• timeLog() consider moving timeLog() from the info to the log section in the severity table