Added download URLs for the manual in PDF, HTML, and EPUB format.
Added the Google Analytics tracking code for libcpr.org.
Squashed 'doc/manual/.themes/' changes from 8ed3c9e..b5fc871

b5fc871 Customized the HTML page title format in HTML manuals.
8fb46b4 Hid some superfluous functionality for single-page HTML builds.
7832d97 Implemented support for Google Analytics's asynchronous snippet.
febd140 Improved the wording of the search box's placeholder text.
6758943 Updated the CREDITS file to include the 'sphinx_rtd_theme' project.

git-subtree-dir: doc/manual/.themes
git-subtree-split: b5fc8717be01639a2e22dbcc5b4b30ef6ad46f4a
Merged the https://github.com/dryproject/sphinx-themes subtree.