Finishes new error/warning handling, thus closing issue #13.

In particular:

 * Adds output parsing for pandoc, bibtex, gnuplot and makeindex.
 * Messages from engine now come before extensions.
 * Log-line-numbers are now consistent with the aggregated raw log.
 * Log output depends better on message content, e.g. missing information.
 * Adds the possibility for messages to keep their original formatting.
 * Adds "Runaway argument?" errors to TeXLogParser.
 * Adds errors to test files so logs can be tested.

Some small stuff:

 * We now abort completely if the first run fails to produce a result.
 * We also "abort" if an engine needs only one run (e.g. pandoc).
 * Some kinks in CLI output removed.
 * Updates readme and adds remarks about TikZ externalisation.