Add PDF building

This commit add PDF building tox.ini environment and options for LaTeX
output. overview.rst is copied from README.rst. And, the original
README.rst file is shrunk because we don't need such a long information
in the README file. People can see the same contents in overview.rst
now.

Change-Id: Id654c814988e78704726d2ba8bea9a03ce8596f8
diff --git a/tox.ini b/tox.ini
index ca4bb3f..effd400 100644
--- a/tox.ini
+++ b/tox.ini
@@ -268,6 +268,15 @@
   sphinx-build -W -b html doc/source doc/build/html
 whitelist_externals = rm
 
+[testenv:pdf-docs]
+basepython = python3
+deps = {[testenv:docs]deps}
+whitelist_externals =
+   make
+commands =
+   sphinx-build -W -b latex doc/source doc/build/pdf
+   make -C doc/build/pdf
+
 [testenv:pep8]
 deps =
     -r{toxinidir}/test-requirements.txt