Entity decoding in Text tokens

Now the decode function for each will decode HTML entities:

    λ> Text.HTML.TagStream.ByteString.decode "foo bar &quot;mu&lt; zot &hello;"
    Right [Text "foo bar \"mu< zot "]
    λ> Text.HTML.TagStream.Text.decode "foo bar &quot;mu&lt; zot &hello;"
    Right [Text "foo bar \"mu< zot "]

The conduit (thanks to @snoyberg) also works:

    λ> CL.sourceList (T.chunksOf 1 "&gt;") C.$= T.tokenStream C.$$ CL.consume
    [Text ">"]

In the spirit of tagstream-conduit's liberal parsing, invalid or unknown entities are skipped:

    λ> Text.HTML.TagStream.Text.decode "&foo; &bar &quot;mu&lt; zot &hello;"
    Right [Text "  \"mu< zot "]

A test case has been added.