Move functions away from `emysql_util` and into their right modules.

Rather than having emysql_util as a "keep everything that doesn't belong elsewhere", we
now handle it as a real helper module for a lot of work. It is now cleaned up for more than it was.
Deprecate `emysql_util`, move functionality to `emysql`

To build a nice API, we need to hide a lot of internal modules in the code base. The goal
of this change is to make `emysql` the sole entry point for the module and its use. To retain
backwards compatibility, we still handle calls to `emysql_util`, but this use is on a deprecation
track for the next major release.

While here:

* Fix the `emysql_util_SUITE` so it actually tests something. It would accept any output.
* Begin simplifying the code base by removing stuff that is not needed.
Pushing in the missing conversion routine module. Remove tracer.
Update the cover spec, mark modules as private.
Update EDoc.
Go over documentation and update it so we don't refer to deprecated functions.

* Improve documentation a bit as well.
* Clean out test sections not relevant anymore.