Partial method completion at REPL

It would be cool if we could restrict the methods list by the types of the arguments:

```
julia> a = 1;

julia> dot(a,\t
dot(x::Number,y::Number) at linalg/matmul.jl:53
```

It would be really cool if we could use type inference to get the inferred types of not-yet-evaluated arguments:

```
julia> a = 1;

julia> dot(a+1,\t
dot(x::Number,y::Number) at linalg/matmul.jl:53
```
