Added support for latex

[Ulimo]

This change adds support latex output. It also adds support to read an algorithm from a textfile.

This PR fixes #15

A suggestion that could improve this is that

\begin{algorithm}
\caption{...}
\begin{algorithmic}
...
\end{algorithmic}
\end{algorithm}

Would be injected in the future so its not required to change the code as in this example.
The directive could then be used like:

.. pcode:: filename.tex
  :caption: Caption text

filename.tex

\Procedure{Quicksort}{$A, p, r$}
\EndProcedure

This also removes some boilerplate code when designing an algorithm.

[Ulimo]

@xxks-kkk is there anything missing to get this merged in?

[xxks-kkk]

Hello Ulimo, Thanks for the pull request. I haven't had a chance to take a look at it yet. I plan to do it this weekend.

…

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[xxks-kkk]

@Ulimo Can you please update the demo doc to showcase everything works properly? I tried to verify your PR but hit some issues.

In specific, I add the following to conf.py

# -- Options for LaTeX output ---------------------------------------------

latex_elements = {
    # The paper size ('letterpaper' or 'a4paper').
    #
    # 'papersize': 'letterpaper',

    # The font size ('10pt', '11pt' or '12pt').
    #
    # 'pointsize': '10pt',

    # Additional stuff for the LaTeX preamble.
    #
    # 'preamble': '',

    # Latex figure (float) alignment
    #
    # 'figure_align': 'htbp',
}

# Grouping the document tree into LaTeX files. List of tuples
# (source start file, target name, title,
#  author, documentclass [howto, manual, or own class]).
latex_documents = [
    (master_doc, 'sphinxcontrib-pseudocode.tex', 'sphinxcontrib-pseudocode documentation',
     'Zeyuan Hu', 'manual'),
]

and is able to generate the necessary TeX files with the command from docs/ directory

sphinx-build -b latex . _build/latex -T -a -E

After I run make all-pdf from the _build/latex, I hit the following error:

<--- snipped --->
LaTeX Warning: Hyper reference `index:quick-sort' on page 1 undefined on input 
line 94.


LaTeX Warning: Reference `index:quick-sort' on page 1 undefined on input line 9
4.


LaTeX Warning: Hyper reference `index:quick-sort' on page 1 undefined on input 
line 98.


LaTeX Warning: Reference `index:quick-sort' on page 1 undefined on input line 9
8.


LaTeX Warning: Hyper reference `index:test-control-blocks' on page 1 undefined 
on input line 102.


LaTeX Warning: Command \LaTeX invalid in math mode on input line 108.


LaTeX Warning: Command \TeX invalid in math mode on input line 108.

! You can't use `\spacefactor' in math mode.
\@->\spacefactor 
                 \@m {}
l.108 ...} directive contains exactly one \(\LaTeX
                                                  \) algorithmic block:
? 

I'm not sure if this is due to my local setup issue (I don't work with building LaTeX from sphinx-doc).