Add multi-host support

This refactoring includes:
- added multi-host mode support;
- added support for graceful shutdown of the service;
- added support to flush the log buffer as it fills;
- D-Bus service xyz.openbmc_project.HostLogger replaced with SIGUSR1
  signal handler;
- self diagnostic messages now registered via phosphor-logging;
- added unit tests;
- build system migrated from autotools to meson;
- source code aligned with OpenBMC conventions.

Change-Id: If6c1dfde278af685d8563450543a6587a282c7e4
Signed-off-by: Artem Senichev <a.senichev@yadro.com>
diff --git a/meson_options.txt b/meson_options.txt
new file mode 100644
index 0000000..8b3977f
--- /dev/null
+++ b/meson_options.txt
@@ -0,0 +1,4 @@
+# Unit tests support
+option('tests',
+       type: 'feature',
+       description: 'Build tests')