removed options, introduced errorcollection instead, adapted readme, …

[Karl1b]

…adapted tests, made single quotes optional

[DeanPDX]

Hey @Karl1b I tweaked this somewhat. Here's what I added:

• I do think there's value in having options so I added them back. Specifically for the file IO errors, in one code path it bails completely and in the other it's the happy path.
• I am returning an error instead of a complex type. I think this is the more idiomatic way of doing things that people will expect. I am still returning a collection of errors and consumers can interact with the err object as either a string or a collection (see new example I added and new Errors function). This approach was influenced by uber-go/multierr.
• I added errors as variables with notes / examples on how to unwrap them and use errors.Is to handle each error type.

[DeanPDX]

This closes #2