Implemented sensor class

Sensor class was introduced, it monitors
xyz.openbmc_project.Sensor.Value, for change and notifies all
listeners.

Tested:
  - Unit tested with service stub that provides dbus interface
    xyz.openbmc_project.Sensor.Value
  - All changes are delivered to listeners
  - All other unit tests are passing

Change-Id: I8c9d58cc986c1fe2a4d2386815d559814016efa6
Signed-off-by: Krzysztof Grobelny <krzysztof.grobelny@intel.com>
diff --git a/meson.build b/meson.build
index 8d0b018..d3472da 100644
--- a/meson.build
+++ b/meson.build
@@ -29,7 +29,12 @@
     language: 'cpp'
 )
 
-boost = dependency('boost', version: '>=1.74.0', required: false)
+boost = dependency(
+  'boost',
+  version: '>=1.74.0',
+  required: false,
+  modules: ['coroutine'])
+
 if not boost.found()
     subproject('boost', required: false)
     boost  = declare_dependency(include_directories: 'subprojects/boost_1_74_0')
@@ -70,6 +75,7 @@
         'src/persistent_json_storage.cpp',
         'src/report.cpp',
         'src/report_manager.cpp',
+        'src/sensor.cpp',
         'src/sensor_cache.cpp',
     ],
     dependencies: [