Update livereload Invoke task and add docs

Removes the `livereload` dependency from `setup.py`.

Updates the `invoke livereload` task by moving the `livereload` import
into the task function since it is now an optional dependency.

Updates the Invoke section of the documentaion with instructions on
using the `livereload` Invoke task.

docs/publish.rst

@@ -146,6 +146,12 @@ http://localhost:8000/::
 
     invoke serve
 
+To serve the generated site with automatic browser reloading every time a
+change is detected, first ``pip install livereload``, then use the
+following command::
+
+    invoke livereload
+
 If during the ``pelican-quickstart`` process you answered "yes" when asked
 whether you want to upload your site via SSH, you can use the following command
 to publish your site via rsync over SSH::

pelican/tools/templates/tasks.py.jinja2

@@ -7,7 +7,6 @@ import datetime
 
 from invoke import task
 from invoke.util import cd
-from livereload import Server
 from pelican.server import ComplexHTTPRequestHandler, RootedHTTPServer
 from pelican.settings import DEFAULT_CONFIG, get_settings_from_file
 
@@ -90,6 +89,7 @@ def preview(c):
 @task
 def livereload(c):
     """Automatically reload browser tab upon file modification."""
+    from livereload import Server
     build(c)
     server = Server()
     deploy_path = CONFIG['deploy_path']

setup.py

@@ -8,7 +8,7 @@ from setuptools import setup
 
 requires = ['feedgenerator >= 1.9', 'jinja2 >= 2.7', 'pygments', 'docutils',
             'pytz >= 0a', 'blinker', 'unidecode', 'six >= 1.4',
-            'python-dateutil', 'livereload']
+            'python-dateutil']
 
 entry_points = {
     'console_scripts': [