Adding friendly error for when needs misses a type declaration

[jwoertink]

Purpose

fixes #864

Description

This will now throw a compile-time error if you use needs without a proper type declaration like needs title : String.

Here's an example of what it looks like.

Checklist

• - An issue already exists detailing the issue/or feature request that this PR fixes
• - All specs are formatted with crystal tool format spec src
• - Inline documentation has been added and/or updated
• - Lucky builds on docker with ./script/setup
• - All builds and specs pass on docker with ./script/test

[paulcsmith]

Love it!