project: reorganize the structure of the project.

* remove dotnet-tool.json because the project does not rely on any dotnet tools.
* remove Directory.Build.props because the solution has only one project.
* move src/SourceGit to src. It's not needed to put all sources into a subfolder of src since there's only one project.

src/Converters/StringConverters.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Globalization;
+
+using Avalonia.Data.Converters;
+using Avalonia.Styling;
+
+namespace SourceGit.Converters
+{
+    public static class StringConverters
+    {
+        public class ToLocaleConverter : IValueConverter
+        {
+            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                return Models.Locale.Supported.Find(x => x.Key == value as string);
+            }
+
+            public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                return (value as Models.Locale).Key;
+            }
+        }
+
+        public static readonly ToLocaleConverter ToLocale = new ToLocaleConverter();
+
+        public class ToThemeConverter : IValueConverter
+        {
+            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                var theme = (string)value;
+                if (theme.Equals("Light", StringComparison.OrdinalIgnoreCase))
+                {
+                    return ThemeVariant.Light;
+                }
+                else if (theme.Equals("Dark", StringComparison.OrdinalIgnoreCase))
+                {
+                    return ThemeVariant.Dark;
+                }
+                else
+                {
+                    return ThemeVariant.Default;
+                }
+            }
+
+            public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                var theme = (ThemeVariant)value;
+                return theme.Key;
+            }
+        }
+
+        public static readonly ToThemeConverter ToTheme = new ToThemeConverter();
+
+        public class FormatByResourceKeyConverter : IValueConverter
+        {
+            public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                var key = parameter as string;
+                return App.Text(key, value);
+            }
+
+            public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
+            {
+                throw new NotImplementedException();
+            }
+        }
+
+        public static readonly FormatByResourceKeyConverter FormatByResourceKey = new FormatByResourceKeyConverter();
+
+        public static readonly FuncValueConverter<string, string> ToShortSHA =
+            new FuncValueConverter<string, string>(v => v.Length > 10 ? v.Substring(0, 10) : v);
+    }
+}