improve hints on splash; fix quick options saving

[hendriktews]

• add menu entry to disable splash screen to quick options
• add info to the splash screen on how to leave and disable the splash screen
• add Proof-General menu to splash screen, such that the hints on the splash screen make sense
• fix saving of quick options for several options
• the CHANGES entry also describes commit ea0f007
• adapt manual

[hendriktews]

@Matafou @erikmd : With the information about how to disable the splash screen present on the splash screen, I think we can and also should increase the splash screen time again, maybe 3 or 4 seconds. With 1 second, it is impossible to see that there is information about how to disable it. What do you think?
Having said that, I don't care too much and we can also leave as is -- I have disabled the splash screen for decades already.

[erikmd]

With the information about how to disable the splash screen present on the splash screen, I think we can and also should increase the splash screen time again, maybe 3 or 4 seconds. With 1 second, it is impossible to see that there is information about how to disable it. What do you think?

IMHO, I would not come back to a 3--4 seconds delay:

I would just disable the splash feature by default, or ideally (to be less "aggressive") modify the splash feature so that the *Proof General Welcome* buffer is still created, but in the background (i.e. similarly to calling M-x bury-buffer RET).
Both approaches would be an acceptable workaround to me.
WDYT?

[monnier]

FWIW, I'd vote to remove the splash screen. I think it makes sense to display such a thing when the users ask "About Proof-General" or in response to a `M-x proof-general` command (maybe from which the user could choose different backends or some such), but doing it when opening a `.v` file is more annoying (and difficult to implement robustly) than it's worth. For the record, I disabled it the first time I tried to use PG because it caused an error in my setup, probably due to either my minibuffer-only frame or my dedicated windows (I never bothered to track it down nor try and see if it had been fixed in the mean time).

[Matafou]

Agreed. A "about" command would be better.