Make sp-forward-symbol and sp-backward-symbol skip comments.

[pierre-rouleau]

The change diff seems bigger that it really is. The change include:

• A new function: sp-inside-comment that returns non-nil when point is inside comment
• Modification of the sp-forward-symbol`: add form inside the cond form to move forward while in comment in the first loop.
• Modification of the sp-backward-symbol : add form inside the cond form to move backward while in comment in the first loop.

[Fuco1]

Well, this works like that on purpose. If we want such a feature it would need to be behind a feature flag because this is backward incompatible behaviour change. Some 3rd party code might depend on this.

[pierre-rouleau]

Then perhaps it'd be good to document the current behaviour. I'll look at the feature flags and see if I can add that under feature flag.