Initial support for terminal within micro

This commit adds beta support for running a shell or other program
within a micro view.

Use the `> term` command. With no arguments, `term` will open your
shell in interactive mode. You can also run an arbitrary command
with `> term cmd` and the command with be executed and output
shown. One issue at the moment is the terminal window will close
immediately after the process dies.

No mouse events are sent to programs running within micro.

Ref #243

cmd/micro/command.go

@@ -56,6 +56,7 @@ func init() {
 		"Pwd":        Pwd,
 		"Open":       Open,
 		"TabSwitch":  TabSwitch,
+		"Term":       Term,
 		"MemUsage":   MemUsage,
 		"Retab":      Retab,
 		"Raw":        Raw,
@@ -114,12 +115,16 @@ func DefaultCommands() map[string]StrCommand {
 		"pwd":        {"Pwd", []Completion{NoCompletion}},
 		"open":       {"Open", []Completion{FileCompletion}},
 		"tabswitch":  {"TabSwitch", []Completion{NoCompletion}},
+		"term":       {"Term", []Completion{NoCompletion}},
 		"memusage":   {"MemUsage", []Completion{NoCompletion}},
 		"retab":      {"Retab", []Completion{NoCompletion}},
 		"raw":        {"Raw", []Completion{NoCompletion}},
 	}
 }
 
+// CommandEditAction returns a bindable function that opens a prompt with
+// the given string and executes the command when the user presses
+// enter
 func CommandEditAction(prompt string) func(*View, bool) bool {
 	return func(v *View, usePlugin bool) bool {
 		input, canceled := messenger.Prompt("> ", prompt, "Command", CommandCompletion)
@@ -130,6 +135,8 @@ func CommandEditAction(prompt string) func(*View, bool) bool {
 	}
 }
 
+// CommandAction returns a bindable function which executes the
+// given command
 func CommandAction(cmd string) func(*View, bool) bool {
 	return func(v *View, usePlugin bool) bool {
 		HandleCommand(cmd)
@@ -699,6 +706,19 @@ func ReplaceAll(args []string) {
 	Replace(append(args, "-a"))
 }
 
+// Term opens a terminal in the current view
+func Term(args []string) {
+	var err error
+	if len(args) == 0 {
+		err = CurView().StartTerminal([]string{os.Getenv("SHELL"), "-i"})
+	} else {
+		err = CurView().StartTerminal(args)
+	}
+	if err != nil {
+		messenger.Error(err)
+	}
+}
+
 // RunShellCommand executes a shell command and returns the output/error
 func RunShellCommand(input string) (string, error) {
 	args, err := shellwords.Split(input)