Add options for bare-bones use

Start by reading issue #308 and inspecting the existing Try Purescript! menu and code-window flow. Decide whether the project should provide a minimal configuration, an online REPL, or both; done means users can enter simple expressions without first deleting elaborate starter code.

Try Purescript! is similar to many other tools online (examples: https://ocaml.org/play, https://jsfiddle.net, https://vega.github.io/editor/#), with a code window on one side and and output window on the other.

The issue: However, Try Purescript! starts with an elaborate menu, so if a user wants to just try out a few expressions, they have to delete a bunch of text in the code window, first, or select an option from the menu with little code, and then delete the resulting code. (Issue #308 is relevant.)

While it definitely a nice feature to include a set of preloaded code examples (!), it would also be nice to be able to enter simple expressions and see what happens. Options:

• Add a menu option for a minimal code configuration. I supposed there'd need to be a module declaration, and it would be nice to add imports for modules that would include the sorts of functions that would be included in a Haskell, Idris, etc. prelude. This seems like an easy solution.
• Add a separate online REPL, like the ones at https://www.haskell.org or https://tryclojure.org. This is would be nice. It avoids the need to deal with main, do, etc., which many books and tutorials for Haskell-like languages (including Purescript by Example) avoid early on. If Purescript offered an online REPL, it would be good to preload a set of standard prelude-like modules. Otherwise the experience could be frustrating for a user with even minor familiarity with another Haskell-like language.
• Or both. Best of all worlds.

Thanks.