Add command to extract build info from metadata

This will allow to recreate the metadata after patching the FS.

PUBLISHED_FROM=dae228bbf49d71f383e4dc52316cf98aba3914f5

docs/design-concept/events.md

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+---
+title: Events
+---
+

docs/design-concept/intro.md

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+---
+title: Design Concept
+---
+
+Mongoose is a multi-protocol networking library that implements non-blocking,
+asyncronous IO and provides event-based API. It has three basic data structures:
+
+- [`struct mg_mgr`](#TODO) is an event manager that holds all active
+  connections
+- [`struct mg_connection`](#TODO) describes a connection
+- [`struct mbuf`](#TODO) describes data buffer (received or sent data)
+
+Connections could be either *listening*, *outbound* or *inbound*.  Outbound
+connections are created by [`mg_connect()`](#TODO) call.  Listening connections
+are created by [`mg_bind()`](#TODO) call.  Inbound connections are those
+accepted by a listening connection.  Each connection is described by [`struct
+mg_connection`](#TODO) structure, which has a number of fields like socket,
+event handler function, send/receive buffer, flags, et cetera.
+
+Mongoose usage pattern is to declare and initialize event manager, create
+connections and create an event loop by calling [`mg_mgr_poll()`](#TODO) in a
+loop.  [`mg_mgr_poll()`](#TODO) iterates over all sockets, accepts new
+connections, sends and receives data, closes connections, and calls event
+handler functions for the respective events.

docs/design-concept/items.json

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+{
+  "items": [
+    { "type": "markdown", "name": "intro.md" },
+    { "type": "markdown", "name": "memory-buffers.md" }
+  ]
+}

docs/design-concept/memory-buffers.md

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+---
+title: Memory buffers
+---
+
+Each connection has send and receive buffer,
+[`struct mg_connection::send_mbuf`](#TODO)
+and
+[`struct mg_connection::recv_mbuf`](#ODO) respectively.
+When data arrives,
+Mongoose appends received data to the `recv_mbuf` and
+triggers `MG_EV_RECV` event. User may send data back by calling one of the
+output functions, like [`mg_send()`](#TODO) or
+[`mg_printf()`](#TODO). Output functions append data to the
+`send_mbuf`. When Mongoose
+successfully writes data to the socket, it discards data from
+[`mg_connection::send_mbuf`](#TODO) and
+sends `MG_EV_SEND` event. When connection is closed, `MG_EV_CLOSE` event is sent.
+
+![](../../static/img/mongoose/mbuf.png)
+