Fix a compiler ambiguity introduced with a floating point frequency option
for tone().  Thanks to @Rob58329 for discovering this and proposing the
fix.

Match original analogWrite behavior by going from 0...1023 (PWMRANGE) and
not 0...1024, and also explicitly set the analogWrite pin to an OUTPUT.
Thanks to @JAndrassy for finding this.

Fixes esp8266#4380 discovered by @cranphin where interrupts were disabled on a
stopWaveform().  Remove that completely and bracket the update of non-atomic
fields in the structure with disable/enable IRQs for safety.

Explicitly cast the frequency, when passed in as an int, to an
unsigned int.  Verified with snippet:
  tone(D1, (int)1000, 500);
  tone(D1, (unsigned int)1000, 500);
  tone(D1, 1000.0, 500);
  tone(D1, (int)1000);
  tone(D1, (unsigned int)1000);
  tone(D1, 1000.0);