Remove config via global variable

[AlecAivazis]

Branching off of the conversation in #192, we should see if we can use variadic configuration functions to remove as much configuration via global variables as possible.

The things we should consider removing from global config:

• Validators to AskOne
• Icon Text
• Help input rune
• PageSize
• Default filter

[ahmetb]

+PageSize

[AlecAivazis]

@ahmetb thanks for the suggestion! I'm curious if that was because you think there is a better default? I pulled 7 out of nowhere so if you have any reason for a particular number, i'd love to hear it

[ahmetb]

I don't need a better default. :) I just need to configure it per-question.

[AlecAivazis]

Well you can already configure it per prompt by setting the PageSize field on the Select and MultiSelect structs but I'm adding the ability to set it with an AskOpt now