Pre-emptive error notices.

[AnnaBeers]

A certain art when writing code is making sure that when your code hits an error, you have a vague understanding of why that error occurred. I have not yet mastered that art.

There are several instances in DeepNeuro where you may hit a bug because you had a typo in your inputs, or otherwise formatted your data incorrectly. The fact that you did this may not be obvious. Here are some common ones that I will address in the future.

• Filepath checking. Always check and raise errors if a provided folder or filepath does not exist.
• Datasize checking. Raise errors if different channels of input data do not much in dimensions before downstream errors.

We should all add more types of these errors to catch in advance to this issue; I will post updates as they are addressed.

[AnnaBeers]

Referenced in #23

[AnnaBeers]

Most relevant sections for error-checking:

The data submodule, which could check and catch data format errors early,
And the utilities submodule, which could catch filepath errors earlier.