fixed build for latex/latexpdf target

The document did not want to build using the LaTeX (PDF) builder at all due to the included `isotech.txt` and `mmlalias.txt` (defining unicode entities that LaTeX `inputenc` (with `utf8` or `utf8x` parameter) could handle.

Therefore, a list of unicode character replacements (for those that were used) had to be configured for the LaTeX preamble to make the build work. At the same time the default paper format was set to A4, and the literal indicator "Contents:" from `index.rst` was removed as it leads to two additional (almost) blank pages in the LaTeX build. The modification does not make the HTML build appear to look "weird".

Due to the fact of larger amounts of mathematical markup, it might be worth considering to use

    :math:`a^2 + b^2 = c^2`

style math markup instead?