Add optional unescaping for section names (`\.` → `.`)

[danny-portnov]

Use case

INI files sometimes escape dots in section names using backslash:

[Section\.1]
name = value

In current SharpConfig, the section name remains "Section\.1" (with the backslash). I'd like it to be interpreted as "Section.1" for lookups and to escape automatically when saving.

Proposal

• Add a new option like:

  var options = new ConfigurationOptions {
        UnescapeSectionNames = true
  };
  var cfg = Configuration.LoadFromFile(path, options);

• Parse: convert "\." → "."
• Serialize: convert "." → "\." in section headers
• Add test cases to verify behavior

Benefits

• Easier to write natural lookups:

var sec = cfg["Section.1"]; // works as expected

Let me know what you think or if there's an existing branch for this feature!