Use wxTextProofOptions itself to enable or disable the checks

Remove a separate "bool enable" argument of EnableProofCheck() and use
wxTextProofOptions::IsSpellCheckingEnabled() to decide whether the
checks should be enabled or disabled.

Also remove wxTextProofOptions ctor and provide named static factory
functions for creating the objects of this class with clearly defined
meaning.

samples/text/text.cpp

@@ -1209,7 +1209,11 @@ MyPanel::MyPanel( wxFrame *frame, int x, int y, int w, int h )
     m_enter->SetClientData(const_cast<void*>(static_cast<const void*>(wxS("enter"))));
 
 #if wxUSE_SPELLCHECK
-    if ( !m_enter->EnableProofCheck(true, wxTextProofOptions("en_US").SpellCheck()) )
+    // Enable grammar check just for demonstration purposes (note that it's
+    // only supported under Mac, but spell checking will be enabled under the
+    // other platforms too, if supported). If we didn't want to enable it, we
+    // could omit the EnableProofCheck() argument entirely.
+    if ( !m_enter->EnableProofCheck(wxTextProofOptions::Default().GrammarCheck()) )
     {
         wxMessageDialog error(this,
                                 wxT("Spell checking is not available on this platform or control style."),