improve parsing of desktop entries.

- speed up parsing by not creating nearly as many strings.
- fix basic whitespace handling. fixes #4

goos: linux
goarch: amd64
pkg: github.com/nwg-piotr/nwg-drawer
cpu: AMD Ryzen 7 1800X Eight-Core Processor
BenchmarkDesktopEntryParserOld-16    	   10000	    146094 ns/op
BenchmarkDesktopEntryParser-16       	   26097	     43303 ns/op
PASS
ok  	github.com/nwg-piotr/nwg-drawer	3.090s

xdgdesktop_parser_test.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"strings"
+	"testing"
+)
+
+var result desktopEntry
+
+func BenchmarkDesktopEntryParserOld(b *testing.B) {
+	var entry desktopEntry
+	for n := 0; n < b.N; n++ {
+		entry, _ = parseDesktopEntryFileDeprecated("id", "./desktop-directories/game.directory")
+	}
+	result = entry
+}
+
+func BenchmarkDesktopEntryParser(b *testing.B) {
+	var entry desktopEntry
+	for n := 0; n < b.N; n++ {
+		entry, _ = parseDesktopEntryFile("id", "./desktop-directories/game.directory")
+	}
+	result = entry
+}
+
+func TestWhitespaceHandling(t *testing.T) {
+	const whitespace = `[Desktop Entry]
+	Categories = Debugger; Development; Git; IDE; Programming; TextEditor; 
+	Comment = Editor for building and debugging modern web and cloud applications
+	Exec = bash -c "code-insiders ~/Workspaces/Linux/Flutter.code-workspace"
+	GenericName = Text Editor
+	Icon = vscode-flutter
+	Keywords = editor; IDE; plaintext; text; write; 
+	MimeType = application/x-shellscript; inode/directory; text/english; text/plain; text/x-c; text/x-c++; text/x-c++hdr; text/x-c++src; text/x-chdr; text/x-csrc; text/x-java; text/x-makefile; text/x-moc; text/x-pascal; text/x-tcl; text/x-tex; 
+	Name = VSCode Insiders with Flutter
+	Name[pt] = VSCode Insiders com Flutter
+	StartupNotify = true
+	StartupWMClass = code - insiders
+	Terminal = false
+	NoDisplay = false
+	Type = Application
+	Version = 1.0`
+
+	// entry, err := parseDesktopEntryDeprecated("id", strings.Split(whitespace, "\n"))
+	*lang = "pt"
+	entry, err := parseDesktopEntry("id", strings.NewReader(whitespace))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if entry.Name != "VSCode Insiders with Flutter" {
+		t.Error("failed to parse desktop entry name")
+	}
+
+	if entry.NameLoc != "VSCode Insiders com Flutter" {
+		t.Error("failed to parse localized name")
+	}
+
+	if entry.NoDisplay {
+		t.Error("failed to parse desktop entry no display")
+	}
+}