parity: new PARITY_IGNORE setting (posix/win32)

see #154 for discussion

CHANGES.rst

diff --git a/CHANGES.rst b/CHANGES.rst
index 85633f0..f40d717 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -652,6 +652,7 @@
 Improvements:
 
 - add client mode to exmaple tcp_serial_redirect.py
+- add PARITY_IGNORE ('X'): receive parity bit, but ignore its value
 
 Bugfixes:
 

serial/serialposix.py

diff --git a/serial/serialposix.py b/serial/serialposix.py
index 30af312..27f97f3 100644
--- a/serial/serialposix.py
+++ b/serial/serialposix.py
@@ -360,6 +360,9 @@
         elif self._parity == serial.PARITY_SPACE and plat[:5] == 'linux':
             cflag |= (termios.PARENB | CMSPAR)
             cflag &= ~(termios.PARODD)
+        elif self._parity == serial.PARITY_IGNORE:
+            cflag |= termios.PARENB  # enable parity bit
+            iflag |= termios.IGNPAR  # ignore its value / no error report
         else:
             raise ValueError('Invalid parity: {!r}'.format(self._parity))
         # setup flow control

serial/serialutil.py

diff --git a/serial/serialutil.py b/serial/serialutil.py
index 474b4c2..c2bd774 100644
--- a/serial/serialutil.py
+++ b/serial/serialutil.py
@@ -79,7 +79,7 @@
 LF = to_bytes([10])
 
 
-PARITY_NONE, PARITY_EVEN, PARITY_ODD, PARITY_MARK, PARITY_SPACE = 'N', 'E', 'O', 'M', 'S'
+PARITY_NONE, PARITY_EVEN, PARITY_ODD, PARITY_MARK, PARITY_SPACE, PARITY_IGNORE = 'N', 'E', 'O', 'M', 'S', 'X'
 STOPBITS_ONE, STOPBITS_ONE_POINT_FIVE, STOPBITS_TWO = (1, 1.5, 2)
 FIVEBITS, SIXBITS, SEVENBITS, EIGHTBITS = (5, 6, 7, 8)
 
@@ -116,7 +116,7 @@
                  576000, 921600, 1000000, 1152000, 1500000, 2000000, 2500000,
                  3000000, 3500000, 4000000)
     BYTESIZES = (FIVEBITS, SIXBITS, SEVENBITS, EIGHTBITS)
-    PARITIES = (PARITY_NONE, PARITY_EVEN, PARITY_ODD, PARITY_MARK, PARITY_SPACE)
+    PARITIES = (PARITY_NONE, PARITY_EVEN, PARITY_ODD, PARITY_MARK, PARITY_SPACE, PARITY_IGNORE)
     STOPBITS = (STOPBITS_ONE, STOPBITS_ONE_POINT_FIVE, STOPBITS_TWO)
 
     def __init__(self,

serial/serialwin32.py

diff --git a/serial/serialwin32.py b/serial/serialwin32.py
index 484c4a1..756d921 100644
--- a/serial/serialwin32.py
+++ b/serial/serialwin32.py
@@ -157,6 +157,9 @@
         elif self._parity == serial.PARITY_SPACE:
             comDCB.Parity = win32.SPACEPARITY
             comDCB.fParity = 1  # Enable Parity Check
+        elif self._parity == serial.PARITY_IGNORE:
+            comDCB.Parity = win32.NOPARITY  # ignore the value
+            comDCB.fParity = 1  # Enable Parity bit
         else:
             raise ValueError("Unsupported parity mode: {!r}".format(self._parity))