Use php.ini-production by default

[oliverpool]

Since #19 all the examples use php.ini-production.

I think it would make sense to move this step inside the monica container:

• it removes boilerplates
• it makes default install more secure
• powerusers may still customize the config using $PHP_INI_DIR/conf.d/

I can make a PR if you agree.

[asbiin]

I'm going to close this one as it's recommend (and not complicated) to create your own version of Dockerfile, hence the examples.
See docker-library/php#873