Added space, single-quote char and other chars to the list of chars that fors parameter value

to be quoted when generating icalendar content.
Before generating ical content all double quotes from parameter values are replaced with single quotes,
as it is illegal to have double quotes in parameter values (https://github.com/collective/icalendar/issues/79)
Added tests

src/icalendar/parser.py

@@ -137,7 +137,9 @@ def validate_param_value(value, quoted=True):
         raise ValueError(value)
 
 
-QUOTABLE = re.compile('[,;:].')
+# chars presence of which in parameter value will be cause the value
+# to be enclosed in double-tuotes
+QUOTABLE = re.compile("[,;: ’']")
 
 
 def dQuote(val):
@@ -150,6 +152,9 @@ def dQuote(val):
     >>> dQuote('name:value')
     '"name:value"'
     """
+    # a double-quote character is forbidden to appear in a parameter value
+    # so replace it with a single-quote character
+    val = val.replace('"', "'")
     if QUOTABLE.search(val):
         return '"%s"' % val
     return val

src/icalendar/tests/test_property_params.py

@@ -1,6 +1,9 @@
+# coding: utf-8
+
 import icalendar
 import unittest
 
+
 class TestPropertyParams(unittest.TestCase):
 
     def test_property_params(self):
@@ -19,3 +22,29 @@ class TestPropertyParams(unittest.TestCase):
         # an icalendar string.
         ical2 = icalendar.Calendar.from_ical(ical_str)
         self.assertEqual(ical2.get('ORGANIZER').params.get('CN'), 'Doe, John')
+
+    def test_quoting(self):
+        # not double-quoted
+        self._test_quoting(u"Aramis", 'Aramis')
+        # if a space is present - enclose in double quotes
+        self._test_quoting(u"Aramis Alameda", '"Aramis Alameda"')
+        # a single quote in parameter value - double quote the value
+        self._test_quoting("Aramis d'Alameda", '"Aramis d\'Alameda"')
+        # double quote is replaced with single quote
+        self._test_quoting("Aramis d\"Alameda", '"Aramis d\'Alameda"')
+        self._test_quoting(u"Арамис д'Аламеда", '"Арамис д\'Аламеда"')
+
+    def _test_quoting(self, cn_param, cn_quoted):
+        """
+        @param cn_param: CN parameter value to test for quoting
+        @param cn_quoted: expected quoted parameter in icalendar format
+        """
+        vevent = icalendar.Event()
+        attendee = icalendar.vCalAddress('test@mail.com')
+        attendee.params['CN'] = cn_param
+        vevent.add('ATTENDEE', attendee)
+        self.assertEqual(
+            vevent.to_ical(),
+            'BEGIN:VEVENT\r\nATTENDEE;CN=%s:test@mail.com\r\nEND:VEVENT\r\n'
+            % cn_quoted
+        )