Fix unicode errors triggered by latest version of html5lib.
Fix unicode errors triggered by latest version of html5lib.

With the current versionof html5lib, the simple_footnotes plugin breaks with
an assertion failure. The root causes is that some strings in simple_footnotes
are unicode and others are str type. For html5lib to be happy, everything has
to be unicode.

This patch fixes the html5lib issue, and introduces no other issues I was able
to find.

UHBiocomputation/pelican-plugins,UHBiocomputation/pelican-plugins,mikitex70/pelican-plugins,prisae/pelican-plugins,mortada/pelican-plugins,farseerfc/pelican-plugins,mortada/pelican-plugins,mikitex70/pelican-plugins,andreas-h/pelican-plugins,talha131/pelican-plugins,rlaboiss/pelican-plugins,pxquim/pelican-plugins,danmackinlay/pelican-plugins,mikitex70/pelican-plugins,publicus/pelican-plugins,UHBiocomputation/pelican-plugins,farseerfc/pelican-plugins,talha131/pelican-plugins,pxquim/pelican-plugins,howthebodyworks/pelican-plugins,MarkusH/pelican-plugins,wilsonfreitas/pelican-plugins,rlaboiss/pelican-plugins,M157q/pelican-plugins,gjreda/pelican-plugins,mitchins/pelican-plugins,talha131/pelican-plugins,wilsonfreitas/pelican-plugins,danmackinlay/pelican-plugins,M157q/pelican-plugins,M157q/pelican-plugins,gjreda/pelican-plugins,florianjacob/pelican-plugins,prisae/pelican-plugins,howthebodyworks/pelican-plugins,xsteadfastx/pelican-plugins,talha131/pelican-plugins,mortada/pelican-plugins,florianjacob/pelican-plugins,jantman/pelican-plugins,ingwinlu/pelican-plugins,ingwinlu/pelican-plugins,howthebodyworks/pelican-plugins,ingwinlu/pelican-plugins,prisae/pelican-plugins,wilsonfreitas/pelican-plugins,howthebodyworks/pelican-plugins,MarkusH/pelican-plugins,andreas-h/pelican-plugins,UHBiocomputation/pelican-plugins,farseerfc/pelican-plugins,M157q/pelican-plugins,pxquim/pelican-plugins,danmackinlay/pelican-plugins,publicus/pelican-plugins,publicus/pelican-plugins,MarkusH/pelican-plugins,benjaminabel/pelican-plugins,mortada/pelican-plugins,MarkusH/pelican-plugins,andreas-h/pelican-plugins,publicus/pelican-plugins,mitchins/pelican-plugins,xsteadfastx/pelican-plugins,florianjacob/pelican-plugins,gjreda/pelican-plugins,mortada/pelican-plugins,mikitex70/pelican-plugins,prisae/pelican-plugins,jantman/pelican-plugins,jantman/pelican-plugins,ingwinlu/pelican-plugins,andreas-h/pelican-plugins,xsteadfastx/pelican-plugins,jantman/pelican-plugins,benjaminabel/pelican-plugins,talha131/pelican-plugins,benjaminabel/pelican-plugins,gjreda/pelican-plugins,benjaminabel/pelican-plugins,MarkusH/pelican-plugins,pxquim/pelican-plugins,mitchins/pelican-plugins,farseerfc/pelican-plugins,florianjacob/pelican-plugins,danmackinlay/pelican-plugins,mitchins/pelican-plugins,rlaboiss/pelican-plugins,farseerfc/pelican-plugins,wilsonfreitas/pelican-plugins,rlaboiss/pelican-plugins,xsteadfastx/pelican-plugins