configure v2: update library and usages

[M-Porter]

Major version changes to the library.

• Changes to how configs are setup: Instead of calling Setup() then Config() to create and get the config, you now just call Setup() providing a reference to your config as the second argument. This better matches the expectations of other functions like json.Unmarshal() and viper.Unmarshal().
• The library no longer maintains an internal copy of the config. The implementer is now required to do so. This allows the library to be more simplistic and is a separation of concerns.
• examples directory has been removed in favor of tests. Tests are the preferred way to show off example usage as they both confirm the library works as intended and shows that the examples are not out dated and do work.
• go get -u github.com/m-porter/configure/v2 will refer to the main branch. Previous version code can be found under v1 branch.

[M-Porter]

Closed and reopened PR to trigger workflow