Add documentation about profiling

CHANGES.md

+2017 July 29 Arnaud Blanchard
+
+Applications
+------------
+
+* blc_channels: remove unused channel has been fixed
+* o_gtk_image [FL32,Y800] add min/max option to scale the pixel values
+* o_gtk_image display the name of the channel in the window's tilte
+* o_gnuplot fix a problem using history with synchronized channel. There is still a small problem while display the time scale
+* New script **e_profile.sh** which displays the graphs of the profiling of differents apps: i.e. 'e_profile.sh image.tsv gradient.tsv display.tsv' ( see profile option of blc_program)
+* Add documentation (`PROFILING.md`) axplaining how to use the new profile option.
+
+Libraries
+---------
+
+* blc_channels fix synchronisation problems
+* blc_program in you can use command with parameter in one line (i.e. in blc_channels i3 display image of channel 3)
+* blc_program add option --profile<filename.tsv> (-~) which record the stat of the execution loop. It can then be displayed with **e_profile.sh**

PROFILING.md

+Profiling
+=========
+
+Description
+-----------
+
+When you use many processes in queue it may be useful to study the sequence of execution and the average time spent for each.
+
+To record this data you can use for each application the option `--profile=<filename.tsv>` (`-~<filename.tsv>`) The file will contain the loop starting time, the execution  starting time ( time once the data is ready) and the duration of the loop.
+
+In first row loop starting time indicate in fact, the moment the application has started. The moment `blc_program_init` has been called.
+
+    #start_time(?s) 	exe_time(?s)    	duration(?s)    	
+    1501244087769618	               0	       0	
+    1501244088341986	1501244088341998	     688	
+    1501244088373970	1501244088373972	     169	
+    1501244088409968	1501244088409969	     174	
+    ...
+
+To graph these data, you can use the **e_profile.sh <filename.tsv> [<filename.tsv> ...]**
+
+This generates a graph showing the sequences of executions and a graph showing the average duration of the loop and the period of exectution of the loop.
+
+Example
+-------
+
+    i_v4l2_camera -~camera.tsv | o_gtk_image -~display.tsv
+    e_profile.sh camera.tsv display.tsv
+
+This will profile the execution of image acquisition and display. Thne it will open two windows with the graph showing the sequence of all the executions and a graph showing the average time
+