Add option to control wrapping

[hadley]

This also provides a straightforward mechanism to add other options to roxygen if need be (options should be reserved strictly for controlling backward compatibility, otherwise it is increases the testing load).

Fixes #132.

[krlmlr]

The log of the last build, line 726, shows:

Possibly mis-spelled fields in DESCRIPTION:
  ‘Roxygen’

Can this become a problem?

[hadley]

That's just a note, so I think it's ok. R-exts says "There is no restriction on the use of other fields not mentioned here (but using other capitalizations of these field names would cause confusion)."

[krlmlr]

Is this the permanent solution, or will there be a nicer syntax like

Roxygen:
    wrap
    other_option=value

?

[hadley]

I'd prefer to stick to R code since it's straightforward to parse.

[bastistician]

I was just wondering if the name Roxygen@R would thus be more appropriate - since somehow consistent with the Authors@R field... However, if there is no plain text equivalent specification, sticking to a pure Roxygen definitely seems nicer.

[hadley]

Yeah, I thought about that too, but on the balance, I think I prefer just Roxygen