- Added hyper as dependency

- Added `go` keyword to syntax
- Added “typechk/go.dyon”
- Added `ast::Expression::Go`
- Added “join_thread” intrinsic
- Added `Thread` struct
- Added `Variable::Thread`
- Added unsafe impl of `Send` for `Variable`
- Made `Module` clone-able by putting `Module::ext_prelude` in `Arc<_>`
- Added `Kind::Go`
- Require `->` on `go` functions in through type check
- Switched from `ThreadRng` to `StdRng` to make new runtime work in
`move || { … }`
- Added `Runtime::go`

This prevents panic when printing out a variable that has no valid
input representation.

- Added “typechk/threads.dyon”
- Infer thread type from function
- Infer numbers from short loops
- Make sift infer type from body
- Removed non-existing typechk test

- Made type checker show an error when result is unused

- Added “typechk/unused_result.dyon”
- Fixed “random” intrinsic

- Added “typechk/unused_result_2.dyon”
- Check type of only one child for some nodes
- Check all expressions in body of a functions that does not return

Infer return type from body of functions that are declared as
mathematical expressions.

- Clean up `Type::Void` usage

The refined returned types inferred by the type checker should be
copied to the AST for more accurate type checking when calling loaded
function declared as mathematical expressions.

- Changed “returns” to a string representing the type
- Added “takes” for each argument representing the type