add smartcase option for smart case sensitive search

Mentioned in #69.

comp.go

@@ -68,6 +68,9 @@ var (
 		"reverse",
 		"noreverse",
 		"reverse!",
+		"smartcase",
+		"nosmartcase",
+		"smartcase!",
 		"wrapscan",
 		"nowrapscan",
 		"wrapscan!",

doc.go

@@ -75,6 +75,7 @@ The following options can be used to customize the behavior of lf:
     ignorecase  boolean  (default off)
     preview     boolean  (default on)
     reverse     boolean  (default off)
+    smartcase   boolean  (default off)
     wrapscan    boolean  (default on)
     scrolloff   integer  (default 0)
     tabstop     integer  (default 8)

docstring.go

@@ -79,6 +79,7 @@ The following options can be used to customize the behavior of lf:
     ignorecase  boolean  (default off)
     preview     boolean  (default on)
     reverse     boolean  (default off)
+    smartcase   boolean  (default off)
     wrapscan    boolean  (default on)
     scrolloff   integer  (default 0)
     tabstop     integer  (default 8)

eval.go

@@ -62,6 +62,12 @@ func (e *setExpr) eval(app *app, args []string) {
 	case "reverse!":
 		gOpts.reverse = !gOpts.reverse
 		app.nav.renew(app.nav.height)
+	case "smartcase":
+		gOpts.smartcase = true
+	case "nosmartcase":
+		gOpts.smartcase = false
+	case "smartcase!":
+		gOpts.smartcase = !gOpts.smartcase
 	case "wrapscan":
 		gOpts.wrapscan = true
 	case "nowrapscan":

nav.go

@@ -370,7 +370,11 @@ func (nav *nav) cd(wd string) error {
 
 func match(pattern, name string) (matched bool, err error) {
 	if gOpts.ignorecase {
-		pattern, name = strings.ToLower(pattern), strings.ToLower(name)
+		lpattern := strings.ToLower(pattern)
+		if !gOpts.smartcase || lpattern == pattern {
+			pattern = lpattern
+			name = strings.ToLower(name)
+		}
 	}
 	if gOpts.globsearch {
 		return filepath.Match(pattern, name)

opts.go

@@ -10,6 +10,7 @@ var gOpts struct {
 	ignorecase bool
 	preview    bool
 	reverse    bool
+	smartcase  bool
 	wrapscan   bool
 	scrolloff  int
 	tabstop    int
@@ -34,6 +35,7 @@ func init() {
 	gOpts.ignorecase = false
 	gOpts.preview = true
 	gOpts.reverse = false
+	gOpts.smartcase = false
 	gOpts.wrapscan = true
 	gOpts.scrolloff = 0
 	gOpts.tabstop = 8