Simplify test suite configuration

Report coverage unconditionally on Travis

pcov is fast enough for this to be acceptable.

Integrate with Codecov

@link in convertException gives 404

The links in convertException gives 404, i'm not 100% if I updated them correct, or if the e.g. should be update to 8.0 already.

https://dev.mysql.com/doc/refman/8.0/en/server-error-reference.html
https://dev.mysql.com/doc/refman/8.0/en/client-error-reference.html

Psalm 6

The php docs are not very clear about that one.

It confuses both Psalm and PHPStan, and involves complicated mocking.

This return type is conditional to $params['wrapperClass']. Luckily,
recent versions of Psalm allow documenting it properly.
See https://github.com/vimeo/psalm/issues/3277

Note that phpstan is not able to understand this yet, but still attempts
to, hence the extra ignore rules.

This hack is temporary and should be removed on 3.0.x

See https://github.com/vimeo/psalm/issues/3224

This is precisely what we are testing here.

This is what is expected with FETCH_COLUMN

That alone fixes 6 issues found by Psalm

Not all RDBMS have a concept of database, apparently (see SQLAnywhere).
Those who do not should pass in a string to stay compatible with the
signature.

The method signature does not allow null.

We are testing what happens when providing the wrong type.