Change download location for Windows from scapy.net to hg repo

The ZIP file available at http://scapy.net/ has an additional header to
make it startable on Linux. This confuses the Windows internal unzipper
and causes warnings about corrupted archives. The files can be
extracted with 7-Zip or InfoUnzip, but this might be inconvenient
for a lot of users. So we now point to the Hg repo which carries
an unmodified ZIP.
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Fixed duplicate reference in install.rst

The duplicate reference "latest version" gave a Sphinx warning.
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Updated version number of Scapy documentation
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Fixed typo in Windows installation doc
2 files changed