* Separated SmartFormat features from `string.Format`compatibility
* Moved `ParserSettings.UseStringFormatCompatibility` to `Settings.UseStringFormatCompatibility` because this does no more apply to the parser only.
* `string.Format` compatibility:
   * SmartFormat acts as a drop-in replacement, and on top allows for named placeholders besides indexed placeholders. Example (note the colon is not escaped):
   * ```csharp
            var now = DateTime.Now;
            var smartFmt = "It is now {Date:yyyy/MM/dd HH:mm:ss}";
            var stringFmt = $"It is now {now.Date:yyyy/MM/dd HH:mm:ss}";
            var formatter = Smart.CreateDefaultSmartFormat();
            formatter.Settings.UseStringFormatCompatibility = true;
            Assert.That(formatter.Format(smartFmt, now), Is.EqualTo(stringFmt));
      ```
   
   * Custom formatters of SmartFormat are not parsed and thus cannot be used
   * Curly braces are escaped the `string.Format` way with `{{` and `}}`
* SmartFormat added feature:
  * As long as special characters (`(){}:\`) are escaped, any character is allowed anywhere. Now this applies also for the colon. Example (note the escaped colon):
   * ```Csharp
            var now = DateTime.Now;
            var smartFmt = @"It is now {Date:yyyy/MM/dd HH\:mm\:ss}";
            var stringFmt = $"It is now {now.Date:yyyy/MM/dd HH:mm:ss}";
            var formatter = Smart.CreateDefaultSmartFormat();
            formatter.Settings.UseStringFormatCompatibility = false;
            Assert.That(formatter.Format(smartFmt, now), Is.EqualTo(stringFmt));
      ```
  * Tests are modified occordingly
* Parser does not process `string[] formatterExtensionNames` any more
  * CTOR does not take `formatterExtensionNames` as argument
  * `Parser.ParseFormat` does not check for a valid formatter name (it's implemented in the formatter anyway)