RFR: Usign perl instead of sed

[Jesper Wilhelmsson]

On Tue, 26 May 2020 21:06:32 GMT, Jesper Wilhelmsson <jwilhelm at openjdk.org> wrote:

> It turns out that different common versions of sed behaves differently so the suggestion here is to replace it with
> perl.

Added a change to use html 4 as pandoc output. There were issues validating the html 5 output.

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PR: https://git.openjdk.java.net/guide/pull/10