Require autocomplete and jump-to-definition

[nobodywasishere]

I've been working on adding a feature to the vscode extension where it will autocomplete requires, and allow you to jump to the file(s), and I was able to do it without invoking the compiler at all (just plain text parsing). It would be great if Crystalline had this feature as well.

Reference for how I accomplished this in vscode:

• https://github.com/crystal-lang-tools/vscode-crystal-lang/blob/259d9a789756edc75ceac54dee2400d4cdbb498f/src2/completion.ts#L46
• https://github.com/crystal-lang-tools/vscode-crystal-lang/blob/259d9a789756edc75ceac54dee2400d4cdbb498f/src2/requires.ts#L25

If you think this is a worthy feature, I can look into adding it to crystalline myself as well.