Announcing CommandLineParser v2.9.0-preview1

CommandLineParser `v2.9.0-preview1` is releases Today (july 24, 2020) with new features.
The package can be downloaded from:

C#: https://www.nuget.org/packages/CommandLineParser/2.9.0-preview1
F#: https://www.nuget.org/packages/CommandLineParser.Fsharp/2.9.0-preview1

What is new in that version, read [Changelog](https://github.com/commandlineparser/commandline/blob/develop/CHANGELOG.md#290-preview1---2020-7-24)

The new features:
- Multi-instance option support.
option can be repeated as:
```$ myprog -t value1 -t value2 -t value3```
Configure Parser as:
```cs
var parser= new Parser(with =>{
with.AllowMultiInstance =true;
});
```
- Move Errors and Value up to the abstract class definition.
you can extract Options object or Parser Errors from ResultSet:
```cs
var result = parser.ParseArguments(args);
//extract Options object and errors
Options options= result.Value;
var Errors = result.Errors;
```
- Add support for flags enums.
see [wiki](https://github.com/commandlineparser/commandline/wiki/Enum-Flags)
- Implement verb aliases.
```cs
[Verb("copy", aliases: new string[] { "cp", "cpy" }, HelpText = "Copy some stuff")]
public class CopyVerb
{
//....
}
```
You can use verb alias:
```
$ myprg copy -f file.txt
$ myprg cp -f file.txt # use alias
$ myprg cpy -f file.txt # use alias
```
- New Unparsing Extension method is added: `FormatCommandLineArgs` to return array of strings.
see [wiki](https://github.com/commandlineparser/commandline/wiki/Unparsing#unparsing-to-array-of-strings)
- New string extension method `SplitArgs` to split commandline string with handling double quote with/o keeping the double quote and ignoring the extra spaces in the string.
```cs
var myargs="-a xyz --name \"path to file\" -b 123";
string[] args =myargs.SplitArgs(); //return {"-a","xyz","--name","path to file", "-b", "123"}
string[] args =myargs.SplitArgs(true); //keep quote and return {"-a","xyz","--name","\"path to file\"", "-b", "123"}
```
- Allow single dash as a value, now it's allowed: `-a - --filename -` .

Beginnen Sie mit CHANGELOG.md beim Eintrag 2.9.0-preview1 und den verlinkten Wiki-Seiten zu Enum Flags und unparsing. Das Issue listet die Funktionen des Releases auf, nennt aber weder eine noch ausstehende Änderung noch eine überprüfbare Definition of Done.

Vom Indexierungsmodell aus dem Issue-Text verfasst.