Add change tab command

This command allows the user to change tab by giving the tab name. This
can be tab completed too. The previous tab is stored in the tabs module
so that when a new tab is created it is still possible to go to the
previous one.

Normal invocation is :ct folder
Previous tab is :ct -

1 files changed, 20 insertions, 5 deletions

diff --git a/lib/ui/tab.go b/lib/ui/tab.go
index 0061472..7808db4 100644
--- a/lib/ui/tab.go
+++ b/lib/ui/tab.go
@@ -29,7 +29,7 @@ func NewTabs() *Tabs {
 	tabs := &Tabs{}
 	tabs.TabStrip = (*TabStrip)(tabs)
 	tabs.TabContent = (*TabContent)(tabs)
-	tabs.history = []int{0}
+	tabs.history = []int{}
 	return tabs
 }
 
@@ -64,7 +64,10 @@ func (tabs *Tabs) Remove(content Drawable) {
 			break
 		}
 	}
-	tabs.Select(tabs.popHistory())
+	index, ok := tabs.popHistory()
+	if ok {
+		tabs.Select(index)
+	}
 	tabs.TabStrip.Invalidate()
 }
 
@@ -90,22 +93,34 @@ func (tabs *Tabs) Select(index int) {
 	}
 
 	if tabs.Selected != index {
+		tabs.pushHistory(tabs.Selected)
 		tabs.Selected = index
-		tabs.pushHistory(index)
 		tabs.TabStrip.Invalidate()
 		tabs.TabContent.Invalidate()
 	}
 }
 
+func (tabs *Tabs) SelectPrevious() bool {
+	index, ok := tabs.popHistory()
+	if !ok {
+		return false
+	}
+	tabs.Select(index)
+	return true
+}
+
 func (tabs *Tabs) pushHistory(index int) {
 	tabs.history = append(tabs.history, index)
 }
 
-func (tabs *Tabs) popHistory() int {
+func (tabs *Tabs) popHistory() (int, bool) {
 	lastIdx := len(tabs.history) - 1
+	if lastIdx < 0 {
+		return 0, false
+	}
 	item := tabs.history[lastIdx]
 	tabs.history = tabs.history[:lastIdx]
-	return item
+	return item, true
 }
 
 func (tabs *Tabs) removeHistory(index int) {