Simplify the Makefile by not having to provide the html tag. #94

Instead we simply pass `not latex` inside the rst for parts that should
be ignored by latex processor.
We need to explicitly add images used by LaTeX. Fixes #94

This is necessary for all files that are not included via
`..image::` but needed in the LaTeX processing.
Merge pull request #102 from dietmarw/t94-simplfy-latex-rule

Simplify the Makefile by not having to provide the html tag. #94