Update docs and fix bugs (#149)

Improved the docs for the 3 main Tactility projects. I also fixed some inaccuracies and bugs in certain APIs as I went through the code.

TactilityHeadless/Source/service/ServiceRegistry.h

@@ -4,17 +4,40 @@
 
 namespace tt::service {
 
-typedef void (*ManifestCallback)(const ServiceManifest*, void* context);
-
 void initRegistry();
 
+/** Register a service.
+ * @param[in] the service manifest
+ */
 void addService(const ServiceManifest* manifest);
+
+/** Unregister a service.
+ * @param[in] the service manifest
+ */
 void removeService(const ServiceManifest* manifest);
 
+/** Start a service.
+ * @param[in] the service id as defined in its manifest
+ * @return true on success
+ */
 bool startService(const std::string& id);
+
+/** Stop a service.
+ * @param[in] the service id as defined in its manifest
+ * @return true on success or false when service wasn't running.
+ */
 bool stopService(const std::string& id);
 
+/** Find a service manifest by its id.
+ * @param[in] id the id as defined in the manifest
+ * @return the matching manifest or nullptr when it wasn't found
+ */
 const ServiceManifest* _Nullable findManifestId(const std::string& id);
+
+/** Find a service by its manifest id.
+ * @param[in] id the id as defined in the manifest
+ * @return the service context or nullptr when it wasn't found
+ */
 ServiceContext* _Nullable findServiceById(const std::string& id);
 
 } // namespace