Some suggestions after investigating Sure

[catriuspham]

So I read through Sure's docs, and realize some things we could do with our library.

• String similarity: this compares the similarity of 2 string. For example, This is a string should look alike tHIS is A strinG
• .be.ok: exactly the same as our .be.truthy but sound better.
• .be.a(type): this is much more general than our current style (be.a.type) as we don't have to implement much.

[hieueastagile]

@catriuspham : Here's my opinion:

• String similarity is great, we can implement it.
• I prefer be.truthy, since we can use be.falsy and it seems more meaningful.
• I don't remember we have be.a.type?

And, I think the explanation system should be our priority for now.

[catriuspham]

@hieueastagile we can do this:

expect(1).to.be.an.integer()
expect('a').to.be.a.string()

What do you mean by explanation system? Is it the same as the DeepExplaination thingy that you mentioned in this PR: https://github.com/EastAgile/robber.py/pull/31?