Merge pull request #256 from scheidan/patch-1

add information about portability of compression

doc/hdf5.md

@@ -106,8 +106,9 @@ g["A", "chunk", (5,5), "compress", 3] = A
 stores the matrix `A` in 5-by-5 chunks and uses a compression level
 `3`. Instead of `"compress"`, you can use `"deflate"` to specify
 [deflate/zlib](http://en.wikipedia.org/wiki/DEFLATE) compression, or
-`"blosc"` to specify [Blosc](http://www.blosc.org/) compress (which is
-generally much faster than deflate); currently, `"compress"`
+`"blosc"` to specify [Blosc](http://www.blo sc.org/) compress. Blosc is
+generally much faster than deflate, however, files with deflate compression are more 
+portable. Currently, `"compress"`
 corresponds to `"blosc"`. Chunking can be useful if you will typically
 extract small segments of an array.  A heuristic chunking is
 automatically used if you specify compression but don't specify