Support Unmarshal into empty interface{}

[moorereason]

Is your feature request related to a problem? Please describe.
While looking at migrating Hugo from BurntSushi to this package, I found that this package doesn't support unmarshaling into an empty interface{}. Returns an error "only a pointer to struct or map can be unmarshaled from TOML."

Describe the solution you'd like
When an empty interface{} is passed to toml.Unmarshal as the v parameter, decode as a map[string]interface{}.

Describe alternatives you've considered
Stick with BurntSushi. 😞

Additional context

• Desired usage: https://play.golang.org/p/CKHM44HsRgP
• JSON stdlib does this: https://play.golang.org/p/oM0Y08WGuf5
• yaml.v3 does this: https://play.golang.org/p/IMAelUFHQ_p (yaml.v2 creates a map[interface{}]interface{}, but that idea was abandoned in v3)

[pelletier]

Totally right, go-toml should be able to do that. At that point I don't see any blocker to support it -- except finding the time to actually do the work.