Dockerfile-72/73: add xdebug back

Merge pull request #164 from mlebrun/xdebug-php72

Dockerfile-72/73: add xdebug back

Tests: fixed Alpine 7.2 and 7.3

Changed:

• Tests, only

Redis: upgraded to 3.1.6 --> 4.2.0

Changed

• Redis driver v3.1.6 --> https://pecl.php.net/package-changelog.php?package=redis&release=4.2.0

PHP 7.3: now supports YAML + NewRelic

Changes:

• PHP 7.3: YAML and NewRelic extensions available for use

Alpine: upgraded variant from PHP 7.1 --> 7.2

Changes

Alpine:

• PHP engine upgraded to 7.2, following Alpine 3.8 base upgrades
• Igbinary upgraded for latest compatibility

Ubuntu:

• No changes

Dockerfile: NewRelic now supports PHP 7.2

New:

• NewRelic enabled on PHP 7.2 variant

Changed:

• Latest Redis stable release 3.1.6

Dockerfile: removed gearman extension

Removed:

Legacy Gearman extension (only affects Ubuntu variants)

Dockerfile: unbreak pecl placement

Fixed:

• PECL had been moved as a recommended package, broke future builds not including recommended packages. Fixed.

Changed:

• 7.2 Dockerfile combines two RUN commands, like other variants.

Dockerfile: 7.2 now considered GA

• Remove Ubuntu installation "recommends" (wasn't anything real, anyway)
• Redis: increment to latest stable
• Alpine: updated all manual package versions to latest stable
• README: PHP 7.2 is now GA

Dockerfile: upgraded to parent 8.1

Changes:

• https://github.com/behance/docker-nginx/releases/tag/8.1.0