Short notation for function types

Function types require quite a lot of keystrokes. The obvious shorthand is
`(uint) -> (uint)`, but our function types are more complicated than javascript's - we also need to specify internal / external, constant, payable (view, pure). Is there a good notation for these?

We could distinguish internal and external by `->` and `=>` and then something like this:

`(uint) [pure,payable]=> (uint)`

The issue proposes shorter notation for Solidity function types, including internal or external visibility and mutability such as pure and payable. Start by reviewing the proposal and its examples, then identify the relevant parser and type-system entry points; done means an agreed notation is specified and implemented with coverage for the listed function-type combinations.

Written by the indexing model from the issue text.