fix(css): remove "text-rendering: optimizeLegibility" which is bad style

`text-rendering: optimizeLegibility` is very slow on Google Chrome.
http://flat.press/develop/2016/02/chrome-freezes/
https://bocoup.com/weblog/text-rendering

Author: azu

public/css/default.css

@@ -63,9 +63,9 @@ div,dl,dt,dd,ul,ol,li,h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6,
 a{color:#2156a5;text-decoration:underline;line-height:inherit}
 a:hover,a:focus{color:#1d4b8f}
 a img{border:none}
-p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;text-rendering:optimizeLegibility}
+p{font-family:inherit;font-weight:400;font-size:1em;line-height:1.6;margin-bottom:1.25em;}
 p aside{font-size:.875em;line-height:1.35;font-style:italic}
-h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Helvetica Neue","Helvetica",Helvetica,Arial,sans-serif;font-weight:300;font-style:normal;color:#ba3925;text-rendering:optimizeLegibility;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
+h1,h2,h3,#toctitle,.sidebarblock>.content>.title,h4,h5,h6{font-family:"Helvetica Neue","Helvetica",Helvetica,Arial,sans-serif;font-weight:300;font-style:normal;color:#ba3925;margin-top:1em;margin-bottom:.5em;line-height:1.0125em}
 h1 small,h2 small,h3 small,#toctitle small,.sidebarblock>.content>.title small,h4 small,h5 small,h6 small{font-size:60%;color:#e99b8f;line-height:0}
 h1{font-size:2.125em}
 h2{font-size:1.6875em}
@@ -172,7 +172,7 @@ p a>code:hover{color:rgba(0,0,0,.9)}
 #content h1>a.link,h2>a.link,h3>a.link,#toctitle>a.link,.sidebarblock>.content>.title>a.link,h4>a.link,h5>a.link,h6>a.link{color:#ba3925;text-decoration:none}
 #content h1>a.link:hover,h2>a.link:hover,h3>a.link:hover,#toctitle>a.link:hover,.sidebarblock>.content>.title>a.link:hover,h4>a.link:hover,h5>a.link:hover,h6>a.link:hover{color:#a53221}
 .audioblock,.imageblock,.literalblock,.listingblock,.stemblock,.videoblock{margin-bottom:1.25em}
-.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{text-rendering:optimizeLegibility;text-align:left;font-family:"DejaVu Serif",serif;font-size:1rem;font-style:italic}
+.admonitionblock td.content>.title,.audioblock>.title,.exampleblock>.title,.imageblock>.title,.listingblock>.title,.literalblock>.title,.stemblock>.title,.openblock>.title,.paragraph>.title,.quoteblock>.title,table.tableblock>.title,.verseblock>.title,.videoblock>.title,.dlist>.title,.olist>.title,.ulist>.title,.qlist>.title,.hdlist>.title{text-align:left;font-family:"DejaVu Serif",serif;font-size:1rem;font-style:italic}
 table.tableblock>caption.title{white-space:nowrap;overflow:visible;max-width:0}
 .paragraph.lead>p,#preamble>.sectionbody>.paragraph:first-of-type p{color:rgba(0,0,0,.85)}
 table.tableblock #preamble>.sectionbody>.paragraph:first-of-type p{font-size:inherit}
@@ -220,7 +220,7 @@ table.pyhltable .linenodiv{background:none!important;padding-right:0!important}
 .quoteblock .quoteblock blockquote{padding:0 0 0 .75em}
 .quoteblock .quoteblock blockquote:before{display:none}
 .verseblock{margin:0 1em 1.25em 1em}
-.verseblock pre{font-family:"Helvetica Neue","Helvetica",Helvetica,Arial,sans-serif;font-size:1.15rem;color:rgba(0,0,0,.85);font-weight:300;text-rendering:optimizeLegibility}
+.verseblock pre{font-family:"Helvetica Neue","Helvetica",Helvetica,Arial,sans-serif;font-size:1.15rem;color:rgba(0,0,0,.85);font-weight:300;}
 .verseblock pre strong{font-weight:400}
 .verseblock .attribution{margin-top:1.25rem;margin-left:.5ex}
 .quoteblock .attribution,.verseblock .attribution{font-size:.9375em;line-height:1.45;font-style:italic}
@@ -356,7 +356,7 @@ pre .conum[data-value]{position:relative;top:-.125em}
 b.conum *{color:inherit!important}
 .conum:not([data-value]):empty{display:none}
 h1,h2{letter-spacing:-.01em}
-dt,th.tableblock,td.content{text-rendering:optimizeLegibility}
+dt,th.tableblock,td.content{}
 p,td.content{letter-spacing:-.01em}
 p strong,td.content strong{letter-spacing:-.005em}
 p,blockquote,dt,td.content{font-size:1.0625rem}