fix for save-logs! to avoid 'GC overhead limit exceeded'

Fixes clojure-liberator#199

Bad qvals in these headers will now cause a 400 status code to be returned.

This drops JDK7, as JDK8 has become the new baseline.

Also, Clojure 1.10.0 drops support for JDK7.

…ld-matrix

Expand build matrix and add new Clojure versions

```
(defresource example
  "This is my awesome resource!"
  ...)
```

…e-docstring

Allow defresource to have a docstring

The `combine` function attempts to add new values to a collection by
merging them. However, for lists and a vectors, a lazy sequence is
returned rather than a list or a vector.

For lists, `(apply list (concat ...` is used instead of `(into ...` in
order to preserve element order for backwards compatibility, as `into`
would put the new elements at the head of the list.

For vectors, `into` is used, as new elements are added to the tail.

The implementation for sets is simplified.

…mbine-results

Improve `combine` to not return lazy sequences

See clojure-liberator#199

Fixes clojure-liberator#199

Handle malformed Accept-Language Accept-Charset & Accept-Encoding

The default modified-since? decision would always evaluate to false
when the request contained an "if-modified-since" header but the
response didn't contain a "last-modified" header. This seems wrong
because the decision is not actually able to determine whether the
resource has been modified or not.

This patch makes it evaluate to true instead which seems more
reasonable in this situation.