Missing functions in Core.Option module

[unekinn]

In https://github.com/MicrosoftDocs/visualfsharpdocs/blob/live/docs/conceptual/core.option-module-[fsharp].md a lot of functions are missing.

I'm not sure which version these were introduced in, but all seem to be present in stable F# as of today. The codebase indicates that some of these have existed for 4+ years.

Functions missing documentation:

• defaultValue
• defaultWith
• orElse
• orElseWith
• contains
• map2
• map3
• flatten
• ofNullable
• ofObj
• toObj

[TysonMN]

And the link to the live hosting of that page is
https://msdn.microsoft.com/en-us/visualfsharpdocs/conceptual/core.option-module-%5bfsharp%5d