sdbusplus match interface changes

[Patrick Williams]

There are three changes that I made recently to the sdbusplus match APIs
that I'd like new code to start using.  I'm going through the existing
openbmc repositories and making the changes to existing code.

1. Namespace move.

    The sdbusplus::server::match namespace is now sdbusplus::bus::match,
    but there is a temporary alias for the old namespace still in place.
    Once I get all changes merged in the user repositories, I'll remove
    the alias.

    This change was proposed by someone outside OpenBMC that was using
    the library.  I agreed that the 'match' utilities should not be in
    server because they are just as likely to be used by a dbus-client.

2. Addition of match rule utilities.

    I added a number of utilities in the sdbus::bus::match::rules
    namespace that can be used to create signal match rules instead of
    hand-written C-strings.

    Old example:
        "type='signal',member='JobRemoved',path='/org/freedesktop/systemd1',"
        "interface='org.freedesktop.systemd1.Manager'"

    New example:
        type::signal() + member("JobRemoved") +
        path("/org/freedesktop/systemd1) +
        interface("org.freedesktop.systemd1.Manager)

3. Support for std::function-type callbacks.

    Previously, when you had a class member function you wanted to have as
    the callback for a dbus signal, you needed to make a static member
    trampoline like:

        static int callback(msg, void* context)
        {
            return static_cast<MyClass>(context)->realCallback(msg);
        }

        match m = match(..., &MyClass::callback, this);

    You can now avoid writing the trampoline function by using
    std::mem_fn:

        match m = match(..., std::bind(std::mem_fn(&MyClass::callback),
                                       this, _1));

The first repository I modified to take advantage of these three changes
is phosphor-state-manager.  You can find that review here as an example:
https://gerrit.openbmc-project.xyz/#/c/4092

-- 
Patrick Williams
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