Wildcard key search

[Galaco]

Add support for wildcard key searches. regexp is probably the best way forward here, perhaps masked away with a simplified syntax such as <key>* or *<key>.

I would argue that wildcard searches should be simple; more advanced regex searches should be written by user. The limit to this feature should be wildcard *, the same as targetname wildcards in source engine entities, which follows the same keyvalue rules.