doc: Include zlib constants

doc/api/zlib.markdown

@@ -103,15 +103,6 @@ tradeoffs involved in zlib usage.
       }
     }).listen(1337);
 
-## Constants
-
-<!--type=misc-->
-
-All of the constants defined in zlib.h are also defined on
-`require('zlib')`.  They are described in more detail in the zlib
-documentation.  See <http://zlib.net/manual.html#Constants>
-for more details.
-
 ## zlib.createGzip([options])
 
 Returns a new [Gzip](#zlib_class_zlib_gzip) object with an
@@ -232,8 +223,8 @@ relevant when compressing, and are ignored by the decompression classes.
 * strategy (compression only)
 * dictionary (deflate/inflate only, empty dictionary by default)
 
-See the description of `deflateInit2` and `inflateInit2` at
-<http://zlib.net/manual.html#Advanced> for more information on these.
+See the description of `deflateInit2` and `inflateInit2`
+at <http://zlib.net/manual.html#Advanced> for more information on these.
 
 ## Memory Usage Tuning
 
@@ -274,3 +265,69 @@ In general, greater memory usage options will mean that node has to make
 fewer calls to zlib, since it'll be able to process more data in a
 single `write` operation.  So, this is another factor that affects the
 speed, at the cost of memory usage.
+
+## Constants
+
+<!--type=misc-->
+
+All of the constants defined in zlib.h are also defined on
+`require('zlib')`.
+In the normal course of operations, you will not need to ever set any of
+these.  They are documented here so that their presence is not
+surprising.  This section is taken almost directly from the [zlib
+documentation](http://zlib.net/manual.html#Constants).  See
+<http://zlib.net/manual.html#Constants> for more details.
+
+Allowed flush values.
+
+* `zlib.Z_NO_FLUSH`
+* `zlib.Z_PARTIAL_FLUSH`
+* `zlib.Z_SYNC_FLUSH`
+* `zlib.Z_FULL_FLUSH`
+* `zlib.Z_FINISH`
+* `zlib.Z_BLOCK`
+* `zlib.Z_TREES`
+
+Return codes for the compression/decompression functions. Negative
+values are errors, positive values are used for special but normal
+events.
+
+* `zlib.Z_OK`
+* `zlib.Z_STREAM_END`
+* `zlib.Z_NEED_DICT`
+* `zlib.Z_ERRNO`
+* `zlib.Z_STREAM_ERROR`
+* `zlib.Z_DATA_ERROR`
+* `zlib.Z_MEM_ERROR`
+* `zlib.Z_BUF_ERROR`
+* `zlib.Z_VERSION_ERROR`
+
+Compression levels.
+
+* `zlib.Z_NO_COMPRESSION`
+* `zlib.Z_BEST_SPEED`
+* `zlib.Z_BEST_COMPRESSION`
+* `zlib.Z_DEFAULT_COMPRESSION`
+
+Compression strategy.
+
+* `zlib.Z_FILTERED`
+* `zlib.Z_HUFFMAN_ONLY`
+* `zlib.Z_RLE`
+* `zlib.Z_FIXED`
+* `zlib.Z_DEFAULT_STRATEGY`
+
+Possible values of the data_type field.
+
+* `zlib.Z_BINARY`
+* `zlib.Z_TEXT`
+* `zlib.Z_ASCII`
+* `zlib.Z_UNKNOWN`
+
+The deflate compression method (the only one supported in this version).
+
+* `zlib.Z_DEFLATED`
+
+For initializing zalloc, zfree, opaque.
+
+* `zlib.Z_NULL`