adding y_axis scale function.

The function gives the option to ass full y axis scale to the tree in linear or log setting.

.gitignore

@@ -22,3 +22,9 @@ test_tmp/
 # Coverage files
 .coverage
 htmlcov/
+.idea/workspace.xml
+bash_colors.sh
+.idea/ete.iml
+.idea/misc.xml
+.idea/modules.xml
+.idea/vcs.xml

ete3/treeview/main.py

@@ -248,6 +248,7 @@ def __setitem__(self, i, v):
     #def clear(self):
     #    super(NodeStyle, self).__setitem__("_faces", {})
 
+
 class TreeStyle(object):
     """.. versionadded:: 2.1
 
@@ -362,6 +363,14 @@ class TreeStyle(object):
     :param True show_scale: Include the scale legend in the tree
       image
 
+    :param False y_axis['show']: Include calculated y scale legend in the tree
+      image (relative branch length)
+
+    :param linear y_axis['scale_type']: Defined the type of the y_axis scale log/linear
+
+    :param 1 y_axis['scale_length']: Sets the length of the y_axis scale
+       (recomended to set to: root.get_farthest_leaf()[1], the depth of the farthest leaf)
+
     :param None scale_length: Scale length to be used as reference scale bar
     when visualizing tree. None = automatically adjusted.
 
@@ -528,6 +537,12 @@ def __init__(self):
         self.show_scale = True
         self.scale_length = None
 
+        # Draw Y_axis scale
+        self.y_axis = dict()
+        self.y_axis['show'] = False
+        self.y_axis['scale_type'] = 'linear'
+        self.y_axis['scale_length'] = 1
+
         # Initialize aligned face headers
         self.aligned_header = FaceContainer()
         self.aligned_foot = FaceContainer()