Add graphsvg plugin: inline-SVG charts (replacement for the dead Google Chart API)

[ShaiMagal]

Problem

The graphgooglechartapi plugin builds charts as <img> tags pointing at the
Google Image Charts API (chart.googleapis.com/chart?...), and the country map
via the Google Visualization "geomap". Google shut down the Image Charts API in
March 2019, and the Flash-based GeoMap even earlier, so these charts now render
as broken images on every modern report.

Change

A new graphsvg plugin that is a drop-in replacement: it implements the same
ShowGraph hook and the same graph types, but renders everything locally as
self-contained inline SVG.

• Column charts for month / daysofmonth / daysofweek / hours
  (with week-end shading and a bold "current day" label)
• Pie charts for the top-N sections (oss, browsers, filetypes,
  httpstatus, hosts, â�¦)
• Horizontal ranking bar chart for countries_map, replacing the discontinued
  Flash GeoMap

Why SVG

• No external request, no JavaScript, no CDN â�� charts keep working offline and
  inside static (BuildStaticPages) reports
• No visitor data ever leaves the server (privacy / GDPR friendly)
• Crisp vector output with native <title> hover tooltips
• Compatible with both html and xhtml BuildReportFormat
• No new Perl module dependencies

Usage

Replace the old plugin in your config:

#LoadPlugin="graphgooglechartapi"
LoadPlugin="graphsvg"

graphgooglechartapi is left in place but marked deprecated in
awstats.model.conf, where the new plugin is documented.

Testing

• perl -c clean
• Verified end-to-end against a real Apache log: awstats.pl � -update then
  -output produces inline <svg> for all chart types and zero references
  to chart.googleapis.com
• Visually checked the column, pie and ranking charts

Fixing -> #249