Added a new Helper class

[MrDave1999]

With this new functionality the value of the environment variable can be retrieved through the indexer:

var reader = new EnvReader();
var key1 = reader["KEY1"];
var key2 = reader["KEY2"];

The advantage of this is that you can use dependency injection, either manually or by using a service container such as Microsoft.Extensions.DependencyInjection.

For example:

class ExampleController
{
    private IEnvReader reader;
	
    public ExampleController(IEnvReader reader)
    {
         this.reader = reader;
    }
	
    public void MethodExample()
    {
         var key1 = reader["KEY1"];
         var key2 = reader["KEY2"];
    }
}

The IEnvReader interface also has some auxiliary methods to retrieve the value of an environment variable in a specific format (integer, double, etc.) and warns the client when it does not find the variable. It is true that currently the library already has this functionality but it does not warn the client when it does not find an environment variable.

Methods that do not start with Try (as GetBoolValue, etc.) throw an exception when the environment variable is not found. Methods that start with Try (as TryGetBoolValue), however, return false if the variable is not found, so the client has two options for handling the error.

[MrDave1999]

@rogusdev Could you check this PR? Thanks.

[rogusdev]

I see where you are going with this, and why. Honestly, I am a bit concerned about introducing something so different from how env vars are normally collected. Generally my personal recommendation is to have a class that collects all such values that you need in your application, and pass a version of that around as a mock/fake, instead of mocking out the env vars functionality of the language itself. That said, I can understand. So, my main questions is: are you sure about the index access? It seems like the get methods are the real way people should access such things.

[MrDave1999]

@rogusdev The indexer is just a simpler way to access the environment variable. It would be interesting that the library has a feature like this, it's like in PHP for example, you access the environment variables in this way: $_ENV['KEY1'];.

[rogusdev]

This is not thread safe. You should read up on how to make a singleton thread safe, if you really must have a singleton at all -- I strongly discourage it, personally.

[MrDave1999]

@rogusdev To avoid complications, I have removed the property.