os specific Taskvars file

Now it's possible to have Taskfile_windows.yml or Taskvars_linux.yml
(and others).

Asked in a comment in #46

README.md

@@ -78,8 +78,8 @@ build:
 
 ### OS specific task
 
-If you add a `Taskfile_{{GOOS}}` you can override or amend your taskfile based
-on the operating system.
+If you add a `Taskfile_{{GOOS}}.yml` you can override or amend your taskfile
+based on the operating system.
 
 Example:
 
@@ -99,7 +99,11 @@ build:
     - echo "linux"
 ```
 
-Will print out `linux` and not default
+Will print out `linux` and not default.
+
+It's also possible to have OS specific `Taskvars.yml` file, like
+`Taskvars_windows.yml` or `Taskvars_darwin.yml`. See the
+[variables section](#variables) below.
 
 ### Task directory
 

taskfile.go

@@ -42,12 +42,25 @@ func (e *Executor) readTaskfileData(path string) (tasks map[string]*Task, err er
 }
 
 func (e *Executor) readTaskvars() error {
-	file := filepath.Join(e.Dir, TaskvarsFilePath)
+	var (
+		file           = filepath.Join(e.Dir, TaskvarsFilePath)
+		osSpecificFile = fmt.Sprintf("%s_%s", file, runtime.GOOS)
+	)
 
 	if b, err := ioutil.ReadFile(file + ".yml"); err == nil {
 		if err := yaml.UnmarshalStrict(b, &e.taskvars); err != nil {
 			return err
 		}
 	}
+
+	if b, err := ioutil.ReadFile(osSpecificFile + ".yml"); err == nil {
+		osTaskvars := make(Vars, 10)
+		if err := yaml.UnmarshalStrict(b, &osTaskvars); err != nil {
+			return err
+		}
+		for k, v := range osTaskvars {
+			e.taskvars[k] = v
+		}
+	}
 	return nil
 }