Document extra dependencies (#325)

* add extras_require to setup.py and add optional dependencies on readme

* removing tornado from extras_require

* converting extras_require to a dictionary like it is supposed to be

* flake8

* fixing typo in URLs

* removing an untrue comment in the readme

* Update extras_require keys

Co-authored-by: Poruri Sai Rahul <rporuri@enthought.com>

* making suggested changes, adding tornado as optional dependency, and using pypi links on readme instead of github links

* only using pypi links in readme

Co-authored-by: Poruri Sai Rahul <rporuri@enthought.com>

README.rst

@@ -37,7 +37,19 @@ framework. This project contains no plug-ins. You are free to use:
 Prerequisites
 -------------
 
-The supported versions of Python are Python >= 3.5.
+The supported versions of Python are Python >= 3.5.  Envisage requires:
 
-* `apptools <https://github.com/enthought/apptools>`_
-* `traits <https://github.com/enthought/traits>`_
+* `apptools <https://pypi.org/project/apptools/>`_
+* `traits <https://pypi.org/project/traits/>`_
+
+Envisage has the following optional dependencies:
+
+* `Ipykernel <https://pypi.org/project/ipykernel/>`_
+* `Tornado <https://pypi.org/project/tornado>`_
+* `Pyface <https://pypi.org/project/pyface/>`_
+* `TraitsUI <https://pypi.org/project/traitsui/>`_
+
+To build the full documentation one needs:
+
+* `Sphinx <https://pypi.org/project/Sphinx>`_ version 2.1 or later.
+* The `Enthought Sphinx Theme <https://pypi.org/project/enthought-sphinx-theme>`_.

setup.py

@@ -294,6 +294,12 @@ def get_long_description():
             ]
         },
         install_requires=["apptools", "setuptools", "traits"],
+        extras_require={
+            "docs": ["enthought-sphinx-theme", "Sphinx>=2.1.0,!=3.2.0"],
+            "ipython": ["ipykernel", "tornado"],
+            "test": ["coverage", "flake8"],
+            "ui": ["pyface", "traitsui"],
+        },
         license="BSD",
         packages=find_packages(),
         package_data={