Replace reader tags with functions

[calherries]

This PR is a breaking change. It replaces the reader tags defined in data_readers.clj with functions, per Proposal: use malli=? instead of #hawk/malli etc.

Example of how this changes user code:

- (is (=? #hawk/malli [:map [:a :int]] {:a 1})
+ (is (=? (=?/malli [:map [:a :int]]) {:a 1})

See the full set of differences by comparing the docs.

I chose to name the functions to be alphabetic characters only, like malli and not malli= or malli=?, because they are intended to be required into a user code with (require '[mb.hawk.assert-exprs.approximately-equal :as =?]). =?/malli is sufficient to demonstrate its meaning without more characters.

[qnkhuat]

Even though this repo is not really "popular" and afaik we're the only one who uses it, but IMO we should keep the current reader tags to avoid making this a breaking change, there is no downside for us, right? we could mark them as deprecated as well.

[calherries]

@qnkhuat It's a fair point, I can't fault that logic. I'll add them back but mark them as discouraged. They still shouldn't need to appear in the documentation.