Add auto_start parameter to locate control plugin (#1220)

The locate control plugin doesn't provide a way of auto start, being necessary the user click on plugin button to get they position showed on map.
However the Leaflet plugin gives the possibility of having a auto start simply by doing lc.start(); after plugin is initiation.

Author: fullonic

examples/Plugins.ipynb

@@ -764,8 +764,10 @@
     "## Locate control\n",
     "\n",
     "Adds a control button that when clicked, the user device geolocation is displayed.\n",
+    "For list of all possible keyword options see:\n",
+    "https://github.com/domoritz/leaflet-locatecontrol#possible-options\n",
     "\n",
-    "To work properly in production, the connection needs to be encrypted, otherwise browser will not\n",
+    "To work properly in production, the connection needs to be encrypted (HTTPS), otherwise browser will not\n",
     "allow users to share their location."
    ]
   },
@@ -793,6 +795,9 @@
     "\n",
     "plugins.LocateControl().add_to(m)\n",
     "\n",
+    "# If you want get the user device positon after load the map, set auto_start=True\n",
+    "plugins.LocateControl(auto_start=True).add_to(m)\n",
+    "\n",
     "m"
    ]
   }

folium/plugins/locate_control.py

@@ -20,6 +20,9 @@ class LocateControl(MacroElement):
 
     Parameters
     ----------
+    auto-start : bool, default False
+        When set to True, plugin will be activated on map loading and search for user position.
+        Once user location is founded, the map will automatically centered in using user coordinates.
     **kwargs
         For possible options, see https://github.com/domoritz/leaflet-locatecontrol
 
@@ -45,12 +48,16 @@ class LocateControl(MacroElement):
             var {{this.get_name()}} = L.control.locate(
                 {{this.options | tojson}}
             ).addTo({{this._parent.get_name()}});
+            {% if this.auto_start %}
+                {{this.get_name()}}.start();
+            {% endif %}
         {% endmacro %}
         """)
 
-    def __init__(self, **kwargs):
+    def __init__(self, auto_start=False, **kwargs):
         super(LocateControl, self).__init__()
         self._name = 'LocateControl'
+        self.auto_start = auto_start
         self.options = parse_options(**kwargs)
 
     def render(self, **kwargs):