New command :pprint for outputting paper/slide bits

The command:

:pprint fmt width n

outputs the definition of name n for format FMT, with a screen width of
WIDTH columns.

:pprint fmt width tm

outputs the term TM.

The allowed formats are "html" and "latex".


Sample output:
```
Idris> :pprint latex 80 Vect
\documentclass{article}
\usepackage{fancyvrb}
\usepackage[usenames]{xcolor}
\newcommand{\IdrisData}[1]{\textcolor{red}{#1}}
\newcommand{\IdrisType}[1]{\textcolor{blue}{#1}}
\newcommand{\IdrisBound}[1]{\textcolor{magenta}{#1}}
\newcommand{\IdrisFunction}[1]{\textcolor{green}{#1}}
\newcommand{\IdrisKeyword}[1]{{\underline{#1}}}
\newcommand{\IdrisImplicit}[1]{{\itshape \IdrisBound{#1}}}


\begin{document}
% START CODE
\begin{Verbatim}[commandchars=\\\{\}]
\IdrisKeyword{data} \IdrisType{Vect} : \IdrisType{Nat} -> \IdrisType{Type} -> \IdrisType{Type} \IdrisKeyword{where}
  \IdrisData{Nil} : \IdrisType{Vect} \IdrisData{0} \IdrisImplicit{a}
  \IdrisData{(::)} : \IdrisImplicit{a} -> \IdrisType{Vect} \IdrisImplicit{n} \IdrisImplicit{a} -> \IdrisType{Vect} (\IdrisData{S} \IdrisImplicit{n}) \IdrisImplicit{a}
\end{Verbatim}
% END CODE
\end{document}
Idris> :pprint html 80 Vect
<!doctype html><html><head><style>.idris-data { color: red; } 
.idris-type { color: blue; }
.idris-function {color: green; }
.idris-keyword { font-weight: bold; }
.idris-bound { color: purple; }
.idris-implicit { font-style: italic; }</style></head><body><!-- START CODE --><pre><span class="idris-keyword">data</span> <span class="idris-type" title="">Vect</span> : <span class="idris-type" title="Unary natural numbers">Nat</span> -> <span class="idris-type">Type</span> -> <span class="idris-type">Type</span> <span class="idris-keyword">where</span>
  <span class="idris-data" title="">Nil</span> : <span class="idris-type" title="">Vect</span> <span class="idris-data">0</span> <span class="idris-bound idris-implicit">a</span>
  <span class="idris-data" title="">(::)</span> : <span class="idris-bound idris-implicit">a</span> -> <span class="idris-type" title="">Vect</span> <span class="idris-bound idris-implicit">n</span> <span class="idris-bound idris-implicit">a</span> -> <span class="idris-type" title="">Vect</span> (<span class="idris-data" title="Successor">S</span> <span class="idris-bound idris-implicit">n</span>) <span class="idris-bound idris-implicit">a</span></pre><!-- END CODE --></body></html>
```