Make documentation a first class citizen and switch to markdown

[h-man2]

Is your feature request related to a problem? Please describe.
If one looks at the USE "manual" it is completely outdated (last version is from 2007).
The switch to mardown would couple the documentation and changes, because of

1. Markdown files can be rendered in GitHub, so documentation is integrated inton the project website
2. A final PDF could still be generated so nothing is lost

Describe the solution you'd like
In a frist step: translate the LaTex based documentation to Markdown.
Afterwards add build-step to maven to genrate the PDF-manual and to generate some API-Docs

Describe alternatives you've considered
Further using LatTex.

Additional context
n/a

[h-man2]

Was closed by #22

PDF Generation is questionable. Maybe just stay with GitHub Markdown.