feat: set up configuration

A YAML file is used to set the available feeds.
The CLI args can set the port and the path to the YAML file.

go.mod

@@ -1,3 +1,20 @@
 module github.com/evan-buss/opds-proxy
 
 go 1.22
+
+require (
+	github.com/knadh/koanf/parsers/yaml v0.1.0
+	github.com/knadh/koanf/providers/file v1.0.0
+	github.com/knadh/koanf/v2 v2.1.1
+)
+
+require (
+	github.com/fsnotify/fsnotify v1.7.0 // indirect
+	github.com/go-viper/mapstructure/v2 v2.0.0 // indirect
+	github.com/knadh/koanf/maps v0.1.1 // indirect
+	github.com/knadh/koanf/providers/basicflag v1.0.0
+	github.com/mitchellh/copystructure v1.2.0 // indirect
+	github.com/mitchellh/reflectwalk v1.0.2 // indirect
+	golang.org/x/sys v0.22.0 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+)