Adding a check for multipart forms

[jwoertink]

Fixes #12

This one was kind of wild, and I may have gone a little overboard. Here's what the end result looks like:

This will display the request body exactly as it normally would, except for the uploaded file is replaced with a placeholder <Lucky::UploadedFile. I wanted this to look like it was an instance to sort of give you an idea of where to look for more docs when figuring out these uploaded files.

Without this check, uploaded files that are plain text actually work fine provided they have utf8 safe chararset. When it comes to binary files like images, these will contain some invalid encoding characters so when you call request.body.to_s, it raises an error. Since we store the request body in to the database, we don't want to store the entire file. Instead, we're storing everything but the file, and just leaving a placeholder of what file you were uploading.

[matthewmcgarvey]

Nice 🎉