Rename doc subdirectory to docs for higher consistency with OSS standards

docs/CMakeLists.txt

@@ -0,0 +1,25 @@
+# Building doxygen documentation
+
+find_package(Doxygen)
+
+if(BUILD_DOXYGEN_DOC)
+    if(DOXYGEN_FOUND)
+        configure_file(${CMAKE_CURRENT_SOURCE_DIR}/Doxyfile.in ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile @ONLY)
+
+        add_custom_target(doc
+            COMMAND ${DOXYGEN_EXECUTABLE} ${CMAKE_CURRENT_BINARY_DIR}/Doxyfile
+            WORKING_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
+            COMMENT "Generating API documentation with Doxygen"
+            VERBATIM)
+
+        install(DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}/html DESTINATION ${CMAKE_INSTALL_DOCDIR} OPTIONAL)
+    else()
+        message(WARNING "Documentation enabled, but Doxygen cannot be found")
+    endif()
+endif()
+
+install(FILES sdbus-c++-class-diagram.png
+              sdbus-c++-class-diagram.uml
+              systemd-dbus-config.md
+              using-sdbus-c++.md
+        DESTINATION ${CMAKE_INSTALL_DOCDIR})

docs/sdbus-c++-class-diagram.uml

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+@startuml
+
+package "Public API" <<frame>> #DDDDDD {
+interface IConnection {
+  +requestName()
+  +enterProcessLoop()
+  +leaveProcessLoop()
+}
+
+interface IObject {
+  +registerMethod()
+  +emitSignal()
+}
+
+interface IProxy {
+  +callMethod()
+  +subscribeToSignal()
+  +get/setProperty()
+}
+
+class Message {
+  +serialize(...)
+  +deserialize(...)
+  +send()
+  Type msgType
+}
+}
+
+interface IConnectionInternal {
+  +addObjectVTable()
+  +createMethodCall()
+  +createSignal()
+}
+
+class Connection {
+}
+
+class Object {
+  IConnectionInternal& connection
+  string objectPath
+  List interfaces
+  List methods
+  List signals
+  List properties
+}
+
+class Proxy {
+  IConnectionInternal& connection
+  string destination
+  string objectPath
+  List signalHandlers
+}
+
+IConnection <|-- Connection
+IConnectionInternal  <|- Connection
+IObject <|-- Object
+IProxy <|-- Proxy
+Connection <-- Object : "use"
+Connection <-- Proxy : "use"
+Message <.. Object : "send/receive"
+Message <.. Proxy : "send/receive"
+
+@enduml

docs/systemd-dbus-config.md

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+Systemd and dbus configuration
+=======================
+
+**Table of contents**
+
+1. [Introduction](#introduction)
+2. [Systemd configuration](#systemd-configuration)
+3. [Dbus configuration](#dbus-configuration)
+
+Introduction
+------------
+
+To run executable as a systemd service you may need some additional setup. For example, you may need explicitly allow 
+the usage of your service. Following chapters contain template configurations.
+
+
+Systemd configuration
+---------------------------------------
+
+Filename should use `.service` extension. It also must be placed in configuration directory (/etc/systemd/system in
+Ubuntu 18.04.1 LTS) 
+
+```
+[Unit]
+Description=nameOfService
+
+[Service]
+ExecStart=/path/to/executable
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Dbus configuration
+------------------
+
+Typical default D-Bus configuration does not allow to register services except explicitly allowed. Filename should 
+contain name of your service, e.g `/etc/dbus-1/system.d/org.sdbuscpp.concatenator.conf`. So, here is template
+configuration to use dbus interface under root:
+
+```
+<!DOCTYPE busconfig PUBLIC
+ "-//freedesktop//DTD D-BUS Bus Configuration 1.0//EN"
+ "http://www.freedesktop.org/standards/dbus/1.0/busconfig.dtd">
+<busconfig>
+  <policy user="root">
+    <allow own="org.sdbuscpp.concatenator"/>
+    <allow send_destination="org.sdbuscpp"/>
+    <allow send_interface="org.sdbuscpp.concatenator"/>
+  </policy>
+</busconfig>
+```
+
+If you need access from other user `root` should be substituted by desired username. For more refer to `man dbus-daemon`.