Clarify writing in 'Declarations' section

[ybakos]

This series replaces 'later' with 'to the right of', mentions "indenting or positioning" for clarity, and corrects the name of the evaluate function in the "bad" example to match the function name in the "good" example.

[process-bot]

Thanks for the pull request! Make sure it satisfies this checklist. My human colleagues will appreciate it!

Here is what to expect next, and if anyone wants to comment, keep these things in mind.

[ybakos]

My local branch name should be 703-declarations-case, but I'll leave it as-is. This branch addresses #703 .

[ybakos]

@evancz I humbly request a quick review and merge of this documentation change to style-guide. Thanks for all things Elm!