Make enum values typed strings (#18)

This also moves validation into the parsing process and refactors a bunch of code related to the config.

Reviewed-on: #18
Co-authored-by: Anna Rose Wiggins <annabunches@gmail.com>
Co-committed-by: Anna Rose Wiggins <annabunches@gmail.com>

internal/configparser/deviceconfigphysical.go

@@ -0,0 +1,35 @@
+package configparser
+
+type DeviceConfigPhysical struct {
+	Name       string
+	DeviceName string `yaml:"device_name,omitempty"`
+	DevicePath string `yaml:"device_path,omitempty"`
+	Lock       bool
+}
+
+// TODO: custom yaml unmarshaling is obtuse; do we really need to do all of this work
+// just to set a single default value?
+func (dc *DeviceConfigPhysical) UnmarshalYAML(unmarshal func(data interface{}) error) error {
+	var raw struct {
+		Name       string
+		DeviceName string `yaml:"device_name"`
+		DevicePath string `yaml:"device_path"`
+		Lock       bool   `yaml:"lock,omitempty"`
+	}
+
+	// Set non-standard defaults
+	raw.Lock = true
+
+	err := unmarshal(&raw)
+	if err != nil {
+		return err
+	}
+
+	*dc = DeviceConfigPhysical{
+		Name:       raw.Name,
+		DeviceName: raw.DeviceName,
+		DevicePath: raw.DevicePath,
+		Lock:       raw.Lock,
+	}
+	return nil
+}