Make texcmp work again, including KaTeX logo

Since all the math font test cases use the KaTeX logo, we need that.
I started with the definition of the logo from katex.less, but tweaked that
until it gave a good visual match, in particular a very similar logo width,
no matter the actual numbers.

With that logo, most tests can be compiled again, with the exception of the
one containing illegal functions to test visual error reporting.
That one needs to be explicitely disabled.

test/screenshotter/ss_data.yaml

@@ -52,9 +52,7 @@ Exponents: a^{a^a_a}_{a^a_a}
 FractionTest: \dfrac{a}{b}\frac{a}{b}\tfrac{a}{b}\;-\dfrac12\;1\tfrac12
 Functions: \sin\cos\tan\ln\log
 GreekLetters: \alpha\beta\gamma\omega
-KaTeX:
-    tex: \KaTeX
-    nolatex: There is no LaTeX command for this (yet)
+KaTeX: \KaTeX
 Lap: ab\llap{f}cd\rlap{g}h
 LeftRight: \left( x^2 \right) \left\{ x^{x^{x^{x^x}}} \right.
 LeftRightListStyling: a+\left(x+y\right)-x
@@ -108,6 +106,7 @@ UnsupportedCmds:
     tex: \err\,\frac\fracerr3\,2^\superr_\suberr\,\sqrt\sqrterr
     noThrow: 1
     errorColor: "#dd4c4c"
+    nolatex: deliberately does not compile
 VerticalSpacing:
     pre: potato<br>blah
     tex: x^{\Huge y}z

test/screenshotter/test.tex

@@ -1,6 +1,8 @@
 \documentclass[10pt]{article}
 
 \usepackage{amsmath,amssymb}
+\usepackage[mathscr]{eucal}
+\usepackage{eufrak}
 \usepackage[papersize={133pt,100pt},margin=0.5pt]{geometry}
 \usepackage{color}
 \usepackage{etoolbox}
@@ -9,6 +11,14 @@
 
 \newcommand{\blue}[1]{\textcolor{blue}{#1}}
 
+\DeclareRobustCommand{\KaTeX}{\mbox{%
+K\kern-.26em%
+{\sbox0 T\vbox to\ht0{\kern.05em\hbox%
+  {\fontsize{.75em}{1em}\selectfont A}%
+\vss}}%
+\kern-.23em%
+\TeX}}
+
 % Thanks to http://tex.stackexchange.com/a/26017/16923
 \newtoks\kasizetoks
 \def\kasizecollect#1{\afterassignment\kasizeapply\kasizetoks=\bgroup#1$}