Package plugins

New plugin type implementing SQL Packages. When such a plugin is installed a new package appears.

Plugin info structure has the char * string with the SQL block defining the package. Or two blocks, for declaration and the body separately.

And an array of st_maria_plugin structures defining function plugins that are part of the package. They can be declared in the declaration part, to be accessible from the outside, or not, to be internal.

That is, the main purpose of this plugin to allow compiled server functions to be part of the package not accessible directly.

What schema will this package install itself into? This is not quite clear.