latex parser: add support for cleveref style referencing

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Cleveref uses the commands \Cref, \cref, \Cref* and \cref* to
reference labels. This should not lead to a spelling error.

Example LaTeX code:

\documentclass{article}

\usepackage{hyperref}
\usepackage{cleveref}

\begin{document}

\begin{equation}
  \label{eq:badlyspeltword}
  3 = 2 + 1
\end{equation}

\Cref{eq:badlyspeltword}, or \cref{eq:badlyspeltword}, or \cref*{eq:badlyspeltword}

% also in comments \cref{eq:badlyspeltword}

\end{document}