[layout] Place footnotes at the bottom of the page. (#1830)

This uses a feature introduced by memoir 3.7e, '\feetatbottom',
which makes footnotes appear at the bottom of the page, rather
than immediately following the main text.

Author: tkoeppe

source/layout.tex

@@ -24,6 +24,11 @@
 %% even if \raggedbottom (default) is in effect.
 \addtolength{\topskip}{0pt plus 20pt}
 
+%%--------------------------------------------------
+%% Place footnotes at the bottom of the page, rather
+%% than immediately following the main text.
+\feetatbottom
+
 %%--------------------------------------------------
 %% Paragraph and bullet numbering