Allow multiple config files

[fxposter]

"-config" option now accepts wildcards (ie: it's processed via
go's filepath.Glob) and multiple files with ",":

docker-gen -config /example/a,/example/b,/usr/configs/*

[md5]

I'd prefer to see docker-gen accept multiple -config settings each with their own config file. If you really want to be able to use globbing, it could make sense for the shell to do the globbing and have -config take multiple arguments (greedy up until the next -param).

[fxposter]

Actually, globbing is the first step in the direction I'd like to have - so that multiple application provide templates and configs to single docker-gen instance and so that docker-gen automatically catch file changes and filelist changes and regenerate templates based on new configs/

[md5]

I'm just not a fan of utilities doing their own glob processing of command-line arguments if it can be avoided.

As for docker-gen regenerating templates based on new configs, I don't think you could do that with globs anyways since docker-gen doesn't watch config files for changes. If a directory-based approach were taken, docker-gen could potentially use inotify to watch for config file changes (at least on Linux), but there no way to register an inotify watch for a glob that I'm aware of.

[fxposter]

You could just poll on selected interval for anything ;)

[md5]

I just opened an alternate PR at #84 that supports passing the -config flag multiple times to specify multiple config files. I didn't add the globbing because of the complications I mentioned before, but I think the globbing is orthogonal to supporting multiple config files.

[jwilder]

Closing this in favor of #84.