Refactor to remove helpers package

This commit removes the "helpers" package by moving functions from the
package into the other packages that use them.

CheckPayloadSignature() and ExtractParamater() are simply moved to the
"hook" package.  I'm not sure of the usefulness of having these
functions exported, but I left them allow for now.

ValuesToMap() is moved to the "main" webhook package and renamed to
valuesToMap().

Tests were moved into the "hook" package since we only test
ExtractParameter() right now.

This commit closes adnanh/webhook#12.

webhook.go

@@ -12,7 +12,6 @@ import (
 	"os/exec"
 	"strings"
 
-	"github.com/adnanh/webhook/helpers"
 	"github.com/adnanh/webhook/hook"
 
 	"github.com/codegangsta/negroni"
@@ -143,10 +142,10 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 		}
 
 		// parse headers
-		headers := helpers.ValuesToMap(r.Header)
+		headers := valuesToMap(r.Header)
 
 		// parse query variables
-		query := helpers.ValuesToMap(r.URL.Query())
+		query := valuesToMap(r.URL.Query())
 
 		// parse body
 		var payload map[string]interface{}
@@ -167,7 +166,7 @@ func hookHandler(w http.ResponseWriter, r *http.Request) {
 			if err != nil {
 				log.Printf("error parsing form payload %+v\n", err)
 			} else {
-				payload = helpers.ValuesToMap(fd)
+				payload = valuesToMap(fd)
 			}
 		}
 
@@ -236,3 +235,16 @@ func watchForFileChange() {
 		}
 	}
 }
+
+// valuesToMap converts map[string][]string to a map[string]string object
+func valuesToMap(values map[string][]string) map[string]interface{} {
+	ret := make(map[string]interface{})
+
+	for key, value := range values {
+		if len(value) > 0 {
+			ret[key] = value[0]
+		}
+	}
+
+	return ret
+}