Release 2.0.0

Added features:

• Implement configuration loader #2 #3
• Upgrade package Microsoft.Extensions.Configuration to 3.1.22 (Drops support for .Net core 2.x)

Release 1.1.0

Added features:
- Support multi level configurations with double underscores (__). Thank you mhirasawa-sansan! #1

Improve test coverage

• Add null check for SecretManagerConfigurationSource options
• Improve test coverage

Support .Net Core 2.1 LTS

• Downgrade package Microsoft.Extensions.Configuration to 2.1.1 from 3.1.7 to support .Net Core 2.1

Initial release

• Initial release
• Support fetching configuration from Google Secret Manager