Fix #3082: Add BC for PDO-only fetch modes

CI: Add missing listener for MariaDB @ mysqli

Other drivers (including the cache) never supported fetch modes that are
not listed in `FetchMode`. Converting between the contants is only done
for PDO, so BC only needs to be restored here. PDO will validate the
fetch mode, we don’t have to.

Tests: remove implicit verbose flag

Document the correct way of configuring a MariaDB database with serverVersion

[bug] Don't skip column options.

Add symfony tests listener

It is required when using annotations to detect deprecation errors.

README: Add 2.7, drop 2.5

CS bump to 4.0, imports for global functions & constants

Add tests for column collation to prove it works

Allow dynamic intervals in DATE_ADD & DATE_SUB for SQLite

DateIntervalType (negative support) resolves doctrine/dbal#2578

Improve handling of schemas in SQL Server >= 2008

Drop PCRE x modifier in SqliteSchemaManager (#2885 rework)

Connection parameters are cached hashed

Start SQL Server using a synchronous command to avoid intermittent login failures

Added badges for AppVeyor

See https://github.com/doctrine/dbal/pull/2617#discussion_r177250225.

fix typo

Set Appveyor to use PHP 7.2