Update the project structure to move all golang files to a new `src/`
folder. This keeps all the code located in the same place and easier to
work with.
Update the Makefile and goreleaser config to continue to work with the new
folder structure.
Add support for configuring CLI parameters in the application using a new
`cfg` package. The `cfg` package exports an `AppSettings` struct that
contains the settings the application was run with.
Update the application to use the new CLI parameters to set the db to open
and the port to use for the metrics server.
Add support for setting the app version during build. The app includes a
`-version` flag to print the stored version data.
