Fix hardcoded php.ini path
Initial commit of params for Gentoo
Gentoo does not need additional repos
Rename php_version to php_slot
The Gentoo packages are prefixed with dev-php/pecl-
Transform extensions to USE flags for Gentoo

All built-in extensions are on Gentoo USE flags instead of dedicated
packages. Add code to transform them.
Turn php/apache settings into USE flags as well
Do not pass slot in package name
Reuse name from apache package to avoid duplication.
Avoid redeclaration for OS' where one package provides all SAPIs