line_array insert for eofnewline and make default

Makes the `eofnewline` option enabled by default.

Fixes #1525

internal/buffer/save.go

@@ -112,7 +112,7 @@ func (b *Buffer) saveToFile(filename string, withSudo bool) error {
 	if b.Settings["eofnewline"].(bool) {
 		end := b.End()
 		if b.RuneAt(Loc{end.X, end.Y}) != '\n' {
-			b.Insert(end, "\n")
+			b.insert(end, []byte{'\n'})
 		}
 	}
 

internal/config/settings.go

@@ -191,7 +191,7 @@ var defaultCommonSettings = map[string]interface{}{
 	"cursorline":     true,
 	"diffgutter":     false,
 	"encoding":       "utf-8",
-	"eofnewline":     false,
+	"eofnewline":     true,
 	"fastdirty":      false,
 	"fileformat":     "unix",
 	"filetype":       "unknown",

runtime/help/options.md

@@ -85,9 +85,10 @@ Here are the available options:
 
     default value: `utf-8`
 
-* `eofnewline`: micro will automatically add a newline to the file.
+* `eofnewline`: micro will automatically add a newline to the end of the
+   file if one does not exist.
 
-	default value: `false`
+	default value: `true`
 
 * `fastdirty`: this determines what kind of algorithm micro uses to determine
    if a buffer is modified or not. When `fastdirty` is on, micro just uses a