Document and usage update

README.md

 ## About
 
-View **colored** diff in unified-diff format or **side-by-side** mode with
-**auto pager**.  Requires Python (>= 2.5.0) and `less`.
+View **incremental**, **colored** diff in unified format or in **side by side**
+mode with **auto pager**.  Requires python (>= 2.5.0) and `less`.
 
 ![Default](http://ymattw.github.com/cdiff/img/default.png)
-![Side-by-side](http://ymattw.github.com/cdiff/img/side-by-side.png)
+![Side by side](http://ymattw.github.com/cdiff/img/side-by-side.png)
 
 ## Installation
 
 ## Usage
     
 Just give it a diff (patch) file or pipe a diff to it.  Use option `-s` for
-side-by-side view, and option `-w <N>` to use text width other than default
+side-by-side view, and option `-w N` to set a text width other than default
 `80`.  See examples below
 
 View a diff (patch) file:
 
-    cdiff foo.patch           # view colored udiff
-    cdiff foo.patch -s        # side-by-side
-    cdiff foo.patch -s -w 90  # use text width 90 other than default 80
+    cdiff foo.patch             # view incremental, colored udiff
+    cdiff foo.patch -s          # view in side by side mode
+    cdiff foo.patch -s -w 90    # use text width 90 other than default 80
     
 Read diff from svn:
 
 ## Known issue
 
 - Only support unified format for input diff
-- Side-by-side mode has alignment problem for wide chars
+- Side by side mode has alignment problem for wide chars

src/cdiff.py

 # -*- coding: utf-8 -*-
 
 """
-View colored diff in unified-diff format or side-by-side mode with auto pager.
-Requires Python (>= 2.5.0) and less.
+View incremental, colored diff in unified format or in side by side mode with
+auto pager.  Requires Python (>= 2.5.0) and less.
 
 See demo at homepage: https://github.com/ymattw/cdiff
 """
 if sys.hexversion < 0x02050000:
     sys.stderr.write("ERROR: requires python >= 2.5.0\n")
     sys.exit(1)
-_is_py3 = sys.hexversion >= 0x03000000
+IS_PY3 = sys.hexversion >= 0x03000000
 
 import os
 import re
     import optparse
     import subprocess
 
-    usage = '''
-    %(prog)s [options] [diff]
+    usage = '''%s [options] [diff]''' % os.path.basename(sys.argv[0])
+    description= ('''View incremental, colored diff in unified format or '''
+                  '''in side by side mode with auto pager, read stdin if '''
+                  '''diff (patch) file is not given''')
 
-    View diff (patch) file if given, otherwise read stdin''' % \
-            {'prog': os.path.basename(sys.argv[0])}
-
-    parser = optparse.OptionParser(usage)
+    parser = optparse.OptionParser(usage=usage, description=description)
     parser.add_option('-s', '--side-by-side', action='store_true',
             help=('show in side-by-side mode'))
-    parser.add_option('-w', '--width', type='int', default=80,
-            help='set line width (side-by-side mode only), default is 80')
+    parser.add_option('-w', '--width', type='int', default=80, metavar='N',
+            help='set text width (side-by-side mode only), default is 80')
     opts, args = parser.parse_args()
 
     if len(args) >= 1:
-        if _is_py3:
+        if IS_PY3:
             # Python3 needs the newline='' to keep '\r' (DOS format)
             diff_hdl = open(args[0], mode='rt', newline='')
         else:
             diff_hdl = open(args[0], mode='rt')
     elif sys.stdin.isatty():
-        sys.stderr.write('Try --help option for usage\n')
+        parser.print_help()
         sys.exit(1)
     else:
         diff_hdl = sys.stdin