Fix theme path (out-of-tree-builds)

Closes GH-164

doc/manual-src/en/conf.py.in

@@ -99,7 +99,7 @@ html_theme = 'sphinx_rtd_theme'
 #html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-html_theme_path = ['../../sphinx_themes']
+html_theme_path = ['@srcdir@/../../sphinx_themes']
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".

doc/manual-src/pt/conf.py.in

@@ -99,7 +99,7 @@ html_theme = 'sphinx_rtd_theme'
 #html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-html_theme_path = ['../../sphinx_themes']
+html_theme_path = ['@srcdir@/../../sphinx_themes']
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".

doc/manual-src/ru/conf.py.in

@@ -99,7 +99,7 @@ html_theme = 'sphinx_rtd_theme'
 #html_theme_options = {}
 
 # Add any paths that contain custom themes here, relative to this directory.
-html_theme_path = ['../../sphinx_themes']
+html_theme_path = ['@srcdir@/../../sphinx_themes']
 
 # The name for this set of Sphinx documents.  If None, it defaults to
 # "<project> v<release> documentation".