Fix armnn_external_delegate option parsing

 * Fixed the mechanism in armnn_delegate.cpp which creates the runtime
   options by moving it to DelegateOptions. BackendOptions are used in
   the runtime options as well as in the optimizer options but need
   to be processed separately.
 * Added runtime options to DelegateOptions to make it easier to differ
   between backend options of the runtime and the optimization
 * Updated armnn_external_delegate to use runtime options
 * Added explanations to OptimizerOptions

Signed-off-by: Jan Eilers <jan.eilers@arm.com>
Change-Id: I34235474147def261821e4576dd41a83ad492258
diff --git a/include/armnn/IRuntime.hpp b/include/armnn/IRuntime.hpp
index b89cfd7..93f8b0f 100644
--- a/include/armnn/IRuntime.hpp
+++ b/include/armnn/IRuntime.hpp
@@ -119,6 +119,7 @@
 
         /// Setting this value will override the paths set by the DYNAMIC_BACKEND_PATHS compiler directive
         /// Only a single path is allowed for the override
+        /// It defines the path to search for any [dynamic backend libraries](src/dynamic/README.md).
         std::string m_DynamicBackendsPath;
 
         /// Setting this flag will allow the user to create the Runtime in protected mode.
@@ -158,12 +159,19 @@
                 , m_LocalPacketHandlers()
             {}
 
+            /// Indicates whether external profiling is enabled or not.
             bool        m_EnableProfiling;
+            /// Indicates whether external timeline profiling is enabled or not.
             bool        m_TimelineEnabled;
+            /// Path to a file in which outgoing timeline profiling messages will be stored.
             std::string m_OutgoingCaptureFile;
+            /// Path to a file in which incoming timeline profiling messages will be stored.
             std::string m_IncomingCaptureFile;
+            /// Enable profiling output to file only.
             bool        m_FileOnly;
+            /// The duration at which captured profiling messages will be flushed.
             uint32_t    m_CapturePeriod;
+            /// The format of the file used for outputting profiling data.
             std::string m_FileFormat;
             std::vector<armnn::profiling::ILocalPacketHandlerSharedPtr> m_LocalPacketHandlers;
         };