build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Upgrade waf to version 2.0.19
 * Modernize docs/conf.py
 * Improve README.md and INSTALL.rst

Refs: #5095
Change-Id: Ic0f4f3be07d7266e57d6565a665eb24a757291e8
diff --git a/docs/INSTALL.rst b/docs/INSTALL.rst
index c1d664b..771a07c 100644
--- a/docs/INSTALL.rst
+++ b/docs/INSTALL.rst
@@ -6,38 +6,37 @@
 Prerequisites
 -------------
 
--  Install the `ndn-cxx library <http://named-data.net/doc/ndn-cxx/current/INSTALL.html>`_
-   and its requirements
+Install the `ndn-cxx library <https://named-data.net/doc/ndn-cxx/current/INSTALL.html>`_
+and its prerequisites.
 
-To build manpages and API documentation:
+Optionally, to build manpages and API documentation the following additional dependencies
+need to be installed:
 
--  ``doxygen``
--  ``graphviz``
--  ``python-sphinx``
+-  doxygen
+-  graphviz
+-  sphinx
+-  sphinxcontrib-doxylink
 
 Build
 -----
 
-The following basic commands should be used to build NDNS on Ubuntu:
-
-::
+The following basic commands should be used to build NDNS on Ubuntu::
 
     ./waf configure
     ./waf
     sudo ./waf install
 
-Refer to ``./waf --help`` for more options that can be used during ``configure`` stage and
-how to properly configure and run NFD.
+Refer to ``./waf --help`` for more options that can be used during the ``configure`` stage.
 
 Debug symbols
 +++++++++++++
 
-The default compiler flags enable debug symbols to be included in binaries.  This
-potentially allows more meaningful debugging if NDNS or other tools happen to crash.
+The default compiler flags include debug symbols in binaries. This should provide
+more meaningful debugging information if NDNS or other tools happen to crash.
 
-If it is undesirable, default flags can be easily overridden.  The following example shows
-how to completely disable debug symbols and configure NDNS to be installed into ``/usr``
-with configuration in ``/etc`` folder.
+If this is undesirable, the default flags can be overridden to disable debug symbols.
+The following example shows how to completely disable debug symbols and configure
+NDNS to be installed into ``/usr`` with configuration in the ``/etc`` directory.
 
 ::
 
@@ -48,25 +47,22 @@
 Building documentation
 ----------------------
 
-NDNS tutorials and API documentation can be built using the following commands:
-
-::
+NDNS tutorials and API documentation can be built using the following commands::
 
     # Full set of documentation (tutorials + API) in build/docs
     ./waf docs
 
-    # Only tutorials in `build/docs`
+    # Only tutorials in build/docs
     ./waf sphinx
 
-    # Only API docs in `build/docs/doxygen`
-    ./waf doxgyen
+    # Only API docs in build/docs/doxygen
+    ./waf doxygen
 
+If ``sphinx-build`` is detected during ``./waf configure``, manpages will automatically
+be built and installed during the normal build process (i.e., during ``./waf`` and
+``./waf install``). By default, manpages will be installed into ``${PREFIX}/share/man``
+(the default value for ``PREFIX`` is ``/usr/local``). This location can be changed
+during the ``./waf configure`` stage using the ``--prefix``, ``--datarootdir``, or
+``--mandir`` options.
 
-Manpages are automatically created and installed during the normal build process
-(e.g., during ``./waf`` and ``./waf install``), if ``python-sphinx`` module is detected
-during ``./waf configure`` stage.  By default, manpages are installed into
-``${PREFIX}/share/man`` (where default value for ``PREFIX`` is ``/usr/local``). This
-location can be changed during ``./waf configure`` stage using ``--prefix``,
-``--datarootdir``, or ``--mandir`` options.
-
-For more details, refer to ``./waf --help``.
+For further details, please refer to ``./waf --help``.