Support for | in keywords and symbols, support of namespaced maps, special support for :nil/:true/:false, fixes, formatting, deps bump

[prepor]

Hi! Thank you for this package!

Yes, this PR is about many different things, let me know please, if it's better to make multiple PRs. Nevertheless, changes are split into individual commits.

1. It adds support for | in symbols and keywords. https://github.com/edn-format/edn doesn't mention it in the list of allowed symbols but Clojure support them in EDN reader https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/EdnReader.java#L28 and in the language.

I personally love to use them for "or" meaning, like :number|string. It's a blocker for me, because I can't parse my EDN files currently.

2. It adds support for Namespaced Maps introduced in Clojure 1.9 (https://clojure.org/reference/reader#_maps).

Before this PR Eden parsed such maps as tag. That was incorrect because tag can't start from :.

3. It adds special cases for :nil, :true and :false keywords. Before it was impossible to distinguish them from corresponding "special symbols", like Eden.decode!("true") == Eden.decode!(":true") => true.

It now decodes them to {:keyword, nil/true/false} and support of encoding of such structure.

4. It fixes some tests (sets, float)

5. Format code with mix format mix.exs "lib/**/*.{ex,exs}" "test/**/*.{ex,exs}"

6. Bumps deps & removes exreloader (it doesn't compile for me)