add 'source' command to read a configuration file

Related #97

complete.go

@@ -49,6 +49,7 @@ var (
 		"echo",
 		"cd",
 		"select",
+		"source",
 		"push",
 	}
 

doc.go

@@ -50,6 +50,7 @@ The following commands are provided by lf without default keybindings:
     echo    prints its arguments to the message line
     cd      changes working directory to its argument
     select  changes current file selection to its argument
+    source  reads the configuration file in its argument
     push    simulate key pushes given in its argument
 
 The following command line commands are provided by lf with default

docstring.go

@@ -54,6 +54,7 @@ The following commands are provided by lf without default keybindings:
     echo    prints its arguments to the message line
     cd      changes working directory to its argument
     select  changes current file selection to its argument
+    source  reads and evaluates the file in its argument
     push    simulate key pushes given in its argument
 
 The following command line commands are provided by lf with default

eval.go

@@ -464,6 +464,12 @@ func (e *callExpr) eval(app *app, args []string) {
 		}
 		app.ui.loadFile(app.nav)
 		app.ui.loadFileInfo(app.nav)
+	case "source":
+		if len(e.args) != 1 {
+			app.ui.print("source: requires an argument")
+			return
+		}
+		app.readFile(strings.Replace(e.args[0], "~", gUser.HomeDir, -1))
 	case "push":
 		if len(e.args) != 1 {
 			app.ui.print("push: requires an argument")