Add SpellChecking to NeoChat

Fix #98

src/spellcheckhighlighter.h

@@ -0,0 +1,26 @@
+// Copyright (c) 2020 Christian Mollekopf <mollekopf@kolabsystems.com>
+// SPDX-License-Identifier: LGPL-2.0-or-later
+
+#pragma once
+
+#include <QTextDocument>
+#include <QSyntaxHighlighter>
+#include <Sonnet/Speller>
+#include <Sonnet/GuessLanguage>
+
+class SpellcheckHighlighter: public QSyntaxHighlighter
+{
+public:
+    SpellcheckHighlighter(QTextDocument *parent);
+
+protected:
+    void highlightBlock(const QString &text) override;
+
+private:
+    void autodetectLanguage(const QString &sentence);
+    QTextCharFormat mErrorFormat;
+    QTextCharFormat mQuoteFormat;
+    QScopedPointer<Sonnet::Speller> mSpellchecker;
+    QScopedPointer<Sonnet::GuessLanguage> mLanguageGuesser;
+};
+