Documentation: Move all file format documentation into its own manpage

The documentation is largely unchanged except for adoption into the
standard manpage format.

Base/usr/share/man/man5/clipboard.md

@@ -0,0 +1,51 @@
+## Name
+
+clipboard - Data formats specific to Clipboard and drag & drop
+
+## Clipboard
+
+The clipboard feature works through the Clipboard server, which generally acts as a global storage or three things:
+- a `String` mime type,
+- a (potentially large) block of data, shared as an anonymous file,
+- a `HashMap<String, String>` of arbitrary metadata, depending on the mime type.
+
+See also [`Userland/Libraries/LibGUI/Clipboard.h`](../../../../../Userland/Libraries/LibGUI/Clipboard.h).
+
+## Drag & drop
+
+In contrast to the clipboard, the drag & drop feature works through WindowServer, and a bouquet of data is transmitted:
+- a `[UTF8] String` to be displayed while dragging,
+- a `HashMap<String, ByteBuffer>` map that contains arbitrary data for a variety of possible mime types,
+- a `Gfx::ShareableBitmap` to be displayed while dragging
+
+Drag & drop is most prominently supported by File Manager, Spreadsheet, and Terminal.
+Various applications accept drag & drop to open files.
+
+## glyph/x-fonteditor (Clipboard-only)
+
+Requires the metadata-fields `count` (count of glyphs copied) and `first_glyph` (lowest codepoint that is copied), encoded as decimal strings.
+
+The data contains codepoint (encoded as host-endian u32), width and height (as u8's) and glyph bitmap data. It is encoded in width times height many bytes, either 0 (clear) or 1 (set).
+
+Implemented in `FontEditor::MainWidget::copy_selected_glyphs` and `FontEditor::MainWidget::paste_glyphs`, in [`Userland/Applications/FontEditor/MainWidget.cpp`](../../../../../Userland/Applications/FontEditor/MainWidget.cpp).
+
+## image/x-serenityos (Clipboard-only)
+
+Requires the metadata-fields `width`, `height`, `scale`, `format` (see `Gfx::BitmapFormat`), and `pitch`, encoded as decimal strings.
+
+The data is encoded according to `Gfx::determine_storage_format(BitmapFormat)`, so either as
+BGRx8888, BGRA8888, RGBA8888, or 8-bit palette index. Note that the palette is not transferred.
+
+Implemented in [`Clipboard::set_bitmap` and `Clipboard::DataAndType::as_bitmap()`](../../../../../Userland/Libraries/LibGUI/Clipboard.cpp).
+
+## text/uri-list (Clipboard and drag & drop)
+
+Newline-delimited set of URIs. Used by File Manager, FileSystemModel, and Terminal.
+
+Example:
+
+```
+file:///home/anon/Desktop/Browser
+file:///home/anon/Desktop/Help
+file:///home/anon/Desktop/Home
+```