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/buffer.go

@@ -52,6 +52,7 @@ type Buffer struct {
 	// Stores the last modification time of the file the buffer is pointing to
 	ModTime time.Time
 
+	// NumLines is the number of lines in the buffer
 	NumLines int
 
 	syntaxDef   *highlight.Def
@@ -72,6 +73,8 @@ type SerializedBuffer struct {
 	ModTime      time.Time
 }
 
+// NewBufferFromString creates a new buffer containing the given
+// string
 func NewBufferFromString(text, path string) *Buffer {
 	return NewBuffer(strings.NewReader(text), int64(len(text)), path)
 }
@@ -201,6 +204,8 @@ func NewBuffer(reader io.Reader, size int64, path string) *Buffer {
 	return b
 }
 
+// GetName returns the name that should be displayed in the statusline
+// for this buffer
 func (b *Buffer) GetName() string {
 	if b.name == "" {
 		if b.Path == "" {
@@ -333,6 +338,8 @@ func (b *Buffer) Update() {
 	b.NumLines = len(b.lines)
 }
 
+// MergeCursors merges any cursors that are at the same position
+// into one cursor
 func (b *Buffer) MergeCursors() {
 	var cursors []*Cursor
 	for i := 0; i < len(b.cursors); i++ {
@@ -359,6 +366,7 @@ func (b *Buffer) MergeCursors() {
 	}
 }
 
+// UpdateCursors updates all the cursors indicies
 func (b *Buffer) UpdateCursors() {
 	for i, c := range b.cursors {
 		c.Num = i
@@ -488,6 +496,8 @@ func (b *Buffer) SaveAsWithSudo(filename string) error {
 	return err
 }
 
+// Modified returns if this buffer has been modified since
+// being opened
 func (b *Buffer) Modified() bool {
 	if b.Settings["fastdirty"].(bool) {
 		return b.IsModified
@@ -539,6 +549,7 @@ func (b *Buffer) Line(n int) string {
 	return string(b.lines[n].data)
 }
 
+// LinesNum returns the number of lines in the buffer
 func (b *Buffer) LinesNum() int {
 	return len(b.lines)
 }