Add `function` keyword as an alternative way to define functions in mojo about mojo

[lattner]

Thank you for your interest. Right now we're focused on building out the core model of the language (the type system, major missing features etc) as defined in the roadmap. We can come back and apply a new set of paint when the system is up and running - that's when we'll know how all the features "look" when sitting next to each other. Until then, we're making reasonable starting decisions and avoiding syntactic sugar.

This is a long way to say "let's come back to this later". One guiding principle is that we dont' want many synonyms, so we should pick one thing or other other, not have fn and function.

[lattner]

Also, I'm not sure if you were involved then, but this is what we did with Swift: Swift 1/2 bring in the basic functionality and we repainted everything in Swift 3. I don't expect things to take that long for Mojo, but can give you an mental framework to work with.

[slf188]

Sounds good to me, we'll get back to it later then!

If there's anything I can help with (including the type system, translating documentation) please let me know!

I can sense there is a bright future ahead for Mojo. Kudos! @lattner