mame: improve user experience when running

[mascguy (Christopher Nielsen)]

Presently, when launching Mame, the user is presented with several warnings:

$ mame
Unable to create history.db

Unable to create history.db

This is due to the default Mame configuration, which references read-only directories within the MacPorts tree.

For the next port release, we should improve on this:

• At a minimum, the port notes should mention that a custom user configuration file (.ini) will fix such issues.
• In addition, it would be helpful to provide an example user configuration file.
• And finally, it might also be worth using a default configuration, that references user-writable areas. Say, ~/Library/Application Support/Mame/...