Eta Repl IDE Support

[carymrobbins]

The following Eta Repl commands would be helpful for implementing IDE support -

• [x] :browse - List all names exported by a module.
• [ ] :type-at - Show type at expression. This works in ghci but src spans don't work in eta-repl.
• [ ] :modules - List all visible modules; analogous to ghc-mod's modules command.
• [ ] :find - Search for a name in visible modules; analogous to ghc-mod's find command.
• [ ] :version - Report the numeric version of the eta repl; should match the output of --numeric-version

Also, some improvements could be made for existing commands -

• [ ] :loc-at - Currently only works for names defined in the project; it would be nice if this could locate the source positions of library-defined names, given that the library sources have been downloaded
• [ ] :uses - This only works for module-local names; it would be important for this to at least work across a project. Even better would be if we could support uses of names in library sources, but that's more of a nice-to-have.