Still using BOOL where we need Win32 API compatibility.
Using JSBool instead of BOOL or bool where it matters.
Changed most relevant TRUE/FALSE to true/false too (though it's not as critical).

You shouldn't need to #include <stdbool.h> anywhere now - gen_defs.h should do that automatically/correctly based on the language/version/tool. In C23, stdbool.h isn't even needed for bool/true/false definitions (they're keywords), so we don't bother including stdbool.h in that case.
Microsoft didn't define __STDC_VERSION__ in their older tool chains (even though they were C99 compatible and had stdbool.h), so we use a _MSC_VER check to know that there's a stdbool.h we should use in that case.

For other/old compilers (e.g. Borland C) we #define bool/true/false following the pattern of stdbool.h (doesn't use a typedef).

I didn't convert UIFC yet.

This addresses issue #698

e.g. User.downlaoded_file() will now publish to the appropriate MQTT topic and changes to system.node_list[] will get published to MQTT.

Publish all login-failures to this new topic.

This commit also includes a few 64-bit free disk space fixes in the FTP server.

- Most published messages (besides log entries) have a timestamp (in ISO8601 format) prepended and tab-separated
- The order and number of elements in client messages (list and activities) has been updated, now includes user number
- Server client lists are now published to .../SERVER/client/list
- Server client activities (connect, disconnect, update) are now published to .../SERVER/client/action/#
- Server client count is now published to .../SERVER/client (with the maximum client count, if applicable)
- Server states are now just represented by name (e.g. initializing, ready, stopping, stopped) and not number
- BBS errors are logged to sbbs/BBS/action/error/LEVEL (where LEVEL is the log level name, e.g. "critical" or "error')
- All server hack-attempts, SPAM attempts, logins, logouts, uploads, downloads, are published to sbbs/BBS/action/ACTION/*
- Chat pages are published to sbbs/BBS/action/page/node/#
- New users (on the terminal server) are published to sbbs/BBS/action/newuser
- Posted messages and executed external programs (on the terminal server) are published to sbbs/BBS/action/ACTION/CODE topic
- The event thread started/stopped status is published to .../SERVER/event

Yeah, the wiki will get updated soon to reflect/document all these changes

This can be useful when debugging issues (e.g. crashes) and an MQTT consuming/logging client wasn't connected at the time.

<server>/state is now published directly to the <sever> topic level (the "state" topic goes away).

Moved <bbs-id>/node# topics to <bbs-id>/nodes/# (allows better wild-card subscription per MQTT standards).
Publishing total node count to <bbs-id>/nodes rather than <bbs-id>/node_count

Introduced "publish verbosity" control (defaults to "High") - if you want nice human readable (and sometimes redundant) topic messages, leave this set to "High". To reduce traffic, set to "Low". It's expected that purpose-built Synchronet/MQTT clients should work equally-well with either setting, but when using generic MQTT clients/browser, "high" verbosity is nice. The human-readable node status is only published when "high" verbosity is enabled.

Publishing the BBS name to the <bbs-id> topic, the instance hostname (as configured in sbbs.ini) to the <host> topic. Makes the hierarchy much more clear when using an MQTT browser like MQTT Explorer.

Each Synchronet server is now its own MQTT client. This means there's no
longer any MQTT logic in the Synchronet "hosts" (e.g. sbbscon.c, ctrl/*.cpp)
and none needed for SBBS NT services (they'll "just work" with MQTT).

This also means that just about everything (except for nodes, spam and hack)
is now published per-server (in the sbbs/BBS-ID/hostname/server/ topic branch)
and if you want aggregated totals or client lists, you'll have to do that in
your own MQTT client or dashboard.

I also removed the publishing of thread_count and socket_count topics as
they weren't universally supported across all servers and are of questionable
value. They can be added back later if determined to be useful.

Interestingly, not required for successful MSVC build. <shurg>

I suspecte the circular dependency and include-guards around mqtt.h
and startup.h were going to be a problem.

Now support subscriptions (e.g. recycle topics, node input topics) in SBBSCTRL.
This required a lot of search/replace and fun with circular struct pointers.

The only difference in the data/scheme is that the "error" topic (error log) is now under each server rather than each host. I don't *think* there are any other changes from the MQTT consumer side.

Still not done: subscribing (e.g. support for recycle or node-spy-input via MQTT) and NT services support.

This change also includes a cool feature that will prompt the sysop if there's a timeout (30 seconds) while waiting for servers to shutdown gracefully and giving the sysop the option to abort (Cancel) the wait (and shutdown ungracefully) or continue the wait (OK).

This can be used to clear a 'retained' topic (of any type).

Currently, sbbs.exe only
Includes non-Unix build fix in sbbscon.c for issue introduced in previous commit

Requires libmosquitto (e.g. install mosquitto-dev pkg) and set
in ctrl/main.ini:
[mqtt]
Enabled=true
broker_addr=127.0.0.1
broker_port=1883
qos=0
keepalive=10

Next up: Windows support