remove -noalphadither option from README/vwebp.1

+ vwebp's -help output

this is a future option; missed in:
793368e restore decode API compatibility

Change-Id: If920df2cf8de57ebad93a6b98830562149396d8d

README

@@ -294,7 +294,6 @@ Options are:
   -nofancy ..... don't use the fancy YUV420 upscaler
   -nofilter .... disable in-loop filtering
   -dither <int>  dithering strength (0..100), default=50
-  -noalphadither disable alpha plane dithering
   -mt .......... use multi-threading
   -info ........ print info
   -h     ....... this help message

examples/vwebp.c

@@ -377,7 +377,9 @@ static void Help(void) {
          "  -nofancy ..... don't use the fancy YUV420 upscaler\n"
          "  -nofilter .... disable in-loop filtering\n"
          "  -dither <int>  dithering strength (0..100), default=50\n"
+#if WEBP_DECODER_ABI_VERSION > 0x0203
          "  -noalphadither disable alpha plane dithering\n"
+#endif
          "  -mt .......... use multi-threading\n"
          "  -info ........ print info\n"
          "  -h     ....... this help message\n"

man/vwebp.1

@@ -1,5 +1,5 @@
 .\"                                      Hey, EMACS: -*- nroff -*-
-.TH VWEBP 1 "June 13, 2014"
+.TH VWEBP 1 "July 23, 2014"
 .SH NAME
 vwebp \- decompress a WebP file and display it in a window
 .SH SYNOPSIS
@@ -33,10 +33,11 @@ Disable in-loop filtering.
 Specify a dithering \fBstrength\fP between 0 and 100. Dithering is a
 post-processing effect applied to chroma components in lossy compression.
 It helps by smoothing gradients and avoiding banding artifacts. Default: 50.
-.TP
-.BI \-noalphadither
-By default, quantized transparency planes are dithered during decompression,
-to smooth the gradients. This flag will prevent this dithering.
+.\" TODO(jzern): restore post-v0.4.1
+.\" .TP
+.\" .BI \-noalphadither
+.\" By default, quantized transparency planes are dithered during decompression,
+.\" to smooth the gradients. This flag will prevent this dithering.
 .TP
 .B \-mt
 Use multi-threading for decoding, if possible.