Validate command and parameter names

[MartinHelmut]

Description

Currently you can almost write anything for command and parameter names inside the litr.toml. Those will first be validated on execution and some issues never (e.g. a parameter name with starting hyphen like ---progress are currently not validated). To ensure valid names and help the user early there should be a validation on reading the config file with feedback what is wrong.

One idea also could be to show the user a potential solution/valid name.

Also, command and parameter properties are only validated on execution, but should also be on calling litr --help.

DoD

• Parameter names are validated
• Command names are validated
• Properties are validated on help and execution
• The parsing wiki page is updated: https://github.com/krieselreihe/litr/wiki/Command-line-argument-parsing