This adds support for the following input sequences:
-- --- ` ' `` '' \degree \pounds \maltese
resulting in – — ‘ ’ “ ” ° £ ✠ symbols already present in our fonts.
As part of this modification, the recognition of multiple dashes was moved
from the lexer to the parser.
This is neccessary since in math mode a sequence of hyphens is just a
sequence of minus signs. Just like a pair of apostrophes in math mode is a
double prime not a right double quotation mark.
To make this easier, parseGroup and parseOptionalGroup have been merged.
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.
The same test cases we use for our screenshots from Firefox are now also
being rendered by pdflatex, so the resulting images can be used as reference
for how things are supposed to look (if we concentrate on compatibility with
LaTeX). To make comparisons even easier, the differences between LaTeX and
Firefox snapshots are rendered in a visual way, using different colors.
Discussed in pull request #268.
