[librsvg/hospitality: 77/79] ARCHITECTURE.md - new file with a description of librsvg's internals

[Federico Mena Quintero <federico src gnome org>]

commit 9b95fe46f04af697adb02de5b20b44187545e068
Author: Federico Mena Quintero <federico gnome org>
Date:   Thu Dec 28 12:42:10 2017 -0600

    ARCHITECTURE.md - new file with a description of librsvg's internals

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+Architecture of librsvg
+=======================
+
+This document describes the architecture of librsvg, and future plans
+for it.
+
+# A bit of history
+
+Librsvg is an old library.  It started around 2001, when Eazel (the
+original makers of GNOME's file manager Nautilus) needed a library to
+render SVG images.  At that time the SVG format was being
+standardized, so librsvg grew along with the SVG specification.  This
+is why you will sometimes see references to deprecated SVG features in
+the source code.
+
+Librsvg started as an experiment to use libxml2's new SAX parser, so
+that SVG could be streamed in, instead of first creating a DOM.
+Originally it used libart as a rendering library; this was GNOME's
+first antialiased renderer with alpha compositing.  Later, the
+renderer was replaced with Cairo.
+
+Librsvg started as a C library with an ad-hoc API.  At some point it
+got turned into a GObject library, so that the main `RsvgHandle`
+object defines most of the entry points into the library.  Through
+GObject Introspection, this allows librsvg to be used from other
+programming languages.
+
+In 2016, librsvg started getting ported to Rust.  The plan is to leave
+the C API/ABI intact, but to have as much of the internals as possible
+implemented in Rust.  This way we can use a memory-safe, modern
+language, but retain the traditional API/ABI.
+