Remove the `default` notation for options

The notation was parsing-only and all it did was reorder the arguments for from_option. This creates just a needless divergence between what is written and what is printed. Also, removing it frees the name for maybe introducing a function or notation default with a type like T -> option T -> T.

I volunteer to fix all reverse deps that we know about.

LGTM.

merged

mentioned in commit de797b31

Aside from Iris itself, only Fairis needed patching. Everything else that is under nightly checks didn't use default.

mentioned in merge request !32 (merged)