Support other SQL dialects

[yroc92]

While the config defaults to "postgres", the underlying library supports other SQL dialects. We should allow it to support them. In which case, we might want to rename this repo.

Some changes we'll need to make:

• Add dialect as a config option to indicate sql driver
• Determine which sql drivers we want to use. Here they are
• Update repo name
• Update go module path
• Update certmagic / caddy plugin namespaces (sql instead of postgres)
• Update environment variables to be DB_* instead of POSTGRES_*

[yroc92]

@gabrielmocan these would be breaking changes. Do you have any thoughts on this?
@mholt what's usually the best way to move to a breaking version? Just add tags?

[mholt]

At this very early stage in the project's development (it doesn't even have any tags yet, right?), I would just go ahead and make the changes you need to. It's still in active development, and I bet there are very few users who would be impacted by such changes at this point.

Generally, pre-1.0 you can make breaking changes, and after you tag 1.0, breaking changes go into a /v2 module, then /v3, etc.

So personally, I'd say just go for it and make the changes you need. Don't worry about incrementing major versions quite yet.

[AnTheMaker]

Any updates on this?
This is a great plugin and it would be awesome to have mySQL support in the near future!
Keep up the good work!

[gabrielmocan]

I'm currently overloaded with some daunting tasks but as soon as I clear it out, I'll do my best to extend this work.