modules: modpython: Implement Module.AddCommand()

Currently, there is no usable wrapper for CModCommand for use within
bindings, so this commit adds a proxy class that adds itself as a
callback and allows implementing Python classes to implement commands
via __call__().

A completely synthetic example:

import znc

class foo(znc.Module):
    module_types = [znc.CModInfo.UserModule]

    def OnLoad(self, args, message):
        self.AddHelpCommand()
        self.AddCommand(FooCmd)

        return True

class FooCmd(znc.Command):
    cmd = 'foo'
    args = foo.t_d('bar')
    desc = foo.t_d('baz')

    def __call__(self, line):
        self.GetModule().PutModule('I have been foo’d!')

Fixes https://github.com/znc/znc/issues/198

modules/modpython.cpp

@@ -505,6 +505,25 @@ CPySocket::~CPySocket() {
     Py_CLEAR(m_pyObj);
 }
 
+CPyModule* CPyModCommand::GetModule() {
+    return this->m_pModule;
+}
+
+void CPyModCommand::operator()(const CString& sLine) {
+    PyObject* pyRes = PyObject_CallMethod(
+        m_pyObj, const_cast<char*>("__call__"), const_cast<char*>("s"),
+        sLine.c_str());
+    if (!pyRes) {
+        CString sRetMsg = m_pModPython->GetPyExceptionStr();
+        DEBUG("oops, something went wrong when calling command: " << sRetMsg);
+    }
+    Py_CLEAR(pyRes);
+}
+
+CPyModCommand::~CPyModCommand() {
+    Py_CLEAR(m_pyObj);
+}
+
 template <>
 void TModInfo<CModPython>(CModInfo& Info) {
     Info.SetWikiPage("modpython");