Created Container style (markdown)

Container-style.md

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+This section describes container options that specify its style or look.
+
+## Borders for containers
+
+Containers don't have any borders by default, use one of the following options to instruct Termdash to draw a border around a container.
+
+[[/images/container-api/border_styles.png|border_styles]]
+
+The following code shows two containers with different border styles as shown above. The right container has the keyboard focus so its border is highlighted.
+
+```go
+tb, err := termbox.New()
+if err != nil {
+    panic(err)
+}
+defer tb.Close()
+
+c, err := container.New(
+    t,
+    container.SplitVertical(
+        container.Left(
+            container.Border(linestyle.Light),
+        ),
+        container.Right(
+            container.Border(linestyle.Double),
+        ),
+    ),
+)
+if err != nil {
+    return fmt.Errorf("container.New => %v", err)
+}
+```
+
+### [container.Border](https://godoc.org/github.com/mum4k/termdash/container#Border):
+
+The **container.Border** option is used to enable the border and specify its line style. Refer to the [[Linestyle API|linestyle-api]] for the available line styles.
+
+### [container.BorderColor](https://godoc.org/github.com/mum4k/termdash/container#BorderColor):
+
+The **container.BorderColor** option sets the color of the border. This option takes no effect when the container has no border.
+
+### [container.FocusedColor](https://godoc.org/github.com/mum4k/termdash/container#FocusedColor):
+
+The **container.FocusedColor** option sets the color of the border when the container is focused. This option takes no effect when the container has no border.
+
+### Titles for containers
+
+Containers that have a border can also have a text title displayed in the border. The title isn't visible on a container without border.
+
+[[/images/container-api/border_title.png|border_title]]
+
+The following code shows a container with a title in the border that is aligned to the right.
+
+```go
+tb, err := termbox.New()
+if err != nil {
+    panic(err)
+}
+defer tb.Close()
+
+c, err := container.New(
+    t,
+    container.Border(linestyle.Light),
+    container.BorderTitle("hello world"),
+    container.BorderTitleAlignRight(),
+)
+if err != nil {
+    return fmt.Errorf("container.New => %v", err)
+}
+```
+
+### [container.BorderTitle](https://godoc.org/github.com/mum4k/termdash/container#BorderTitle):
+
+The **container.BorderTitle** option sets the title to display on the container. The title is displayed above the container and aligned according to the following alignment options.
+
+### [container.BorderTitleAlignLeft](https://godoc.org/github.com/mum4k/termdash/container#BorderTitleAlignLeft):
+
+The **container.BorderTitleAlignLeft** option indicates that the container title should be aligned at the top left corner.
+
+### [container.BorderTitleAlignCenter](https://godoc.org/github.com/mum4k/termdash/container#BorderTitleAlignCenter):
+
+The **container.BorderTitleAlignCenter** option indicates that the container title should be aligned at the top and center above the container.
+
+### [container.BorderTitleAlignRight](https://godoc.org/github.com/mum4k/termdash/container#BorderTitleAlignRight):
+
+The **container.BorderTitleAlignRight** option indicates that the container title should be aligned at the top right corner.