Add health collector (#70)

* Add health collector for voltage & temperature
* Run gofmt
* Add help text to health collector

config/config.go

@@ -15,6 +15,7 @@ type Config struct {
 		DHCP    bool `yaml:"dhcp,omitempty"`
 		DHCPL   bool `yaml:"dhcpl,omitempty"`
 		DHCPv6  bool `yaml:"dhcpv6,omitempty"`
+		Health  bool `yaml:"health,omitempty"`
 		Routes  bool `yaml:"routes,omitempty"`
 		POE     bool `yaml:"poe,omitempty"`
 		Pools   bool `yaml:"pools,omitempty"`