enhance: use diff command instead of show command to get changes of selected commit. (#56)

* for merge commit, it will shows all changes compare to the first parent of the selected commit now.

src/Commands/QueryCommitChanges.cs

@@ -1,61 +0,0 @@
-using System.Collections.Generic;
-using System.Text.RegularExpressions;
-
-namespace SourceGit.Commands
-{
-    public partial class QueryCommitChanges : Command
-    {
-        [GeneratedRegex(@"^(\s?[\w\?]{1,4})\s+(.+)$")]
-        private static partial Regex REG_FORMAT();
-
-        public QueryCommitChanges(string repo, string commitSHA)
-        {
-            WorkingDirectory = repo;
-            Context = repo;
-            Args = $"show --name-status {commitSHA}";
-        }
-
-        public List<Models.Change> Result()
-        {
-            Exec();
-            _changes.Sort((l, r) => l.Path.CompareTo(r.Path));
-            return _changes;
-        }
-
-        protected override void OnReadline(string line)
-        {
-            var match = REG_FORMAT().Match(line);
-            if (!match.Success)
-                return;
-
-            var change = new Models.Change() { Path = match.Groups[2].Value };
-            var status = match.Groups[1].Value;
-
-            switch (status[0])
-            {
-                case 'M':
-                    change.Set(Models.ChangeState.Modified);
-                    _changes.Add(change);
-                    break;
-                case 'A':
-                    change.Set(Models.ChangeState.Added);
-                    _changes.Add(change);
-                    break;
-                case 'D':
-                    change.Set(Models.ChangeState.Deleted);
-                    _changes.Add(change);
-                    break;
-                case 'R':
-                    change.Set(Models.ChangeState.Renamed);
-                    _changes.Add(change);
-                    break;
-                case 'C':
-                    change.Set(Models.ChangeState.Copied);
-                    _changes.Add(change);
-                    break;
-            }
-        }
-
-        private readonly List<Models.Change> _changes = new List<Models.Change>();
-    }
-}

src/ViewModels/CommitDetail.cs

@@ -355,7 +355,9 @@ namespace SourceGit.ViewModels
                 _cancelToken.Requested = true;
 
             _cancelToken = new Commands.Command.CancelToken();
-            var cmdChanges = new Commands.QueryCommitChanges(_repo, _commit.SHA) { Cancel = _cancelToken };
+
+            var parent = _commit.Parents.Count == 0 ? "4b825dc642cb6eb9a060e54bf8d69288fbee4904" : _commit.Parents[0];
+            var cmdChanges = new Commands.CompareRevisions(_repo, parent, _commit.SHA) { Cancel = _cancelToken };
             var cmdRevisionFiles = new Commands.QueryRevisionObjects(_repo, _commit.SHA) { Cancel = _cancelToken };
 
             Task.Run(() =>