Extendable vector checkers

[ikitommi]

Instead of magic marker, vector special checking is now extendable.

also, previous version allowed the ... to be anywhere in the expected vector if it was also in the last position. Like:

(contains [1 ... 10 ...]) [1 2]) ; => true (matches only 1 and ::then-some)
(contains [1 ... 10]) [1 2]) ; => false (doesn't do ::them-some at all)

Also, added CHANGELOG.md & CONTRIBUTING.md

[jarppe]

I really like this idea. How ever, now the code base has changed and merging this is not trivial anymore.

Also, I would like to use similar approach with other data structures also.

Lets think about this.