make librend packages for HTML and LaTeX depend on common ancestor package

[lueck]

Right now, common/librend is to be replaced by html/librend for HTML output and for LaTeX, common/librend is not a dependency.

For declaring common components in an abstract manner und thus for the reason of architectural clarity and code cleaness, it would be nice to put these common components in a common ancestor package.

common/librend-base (ancestor), which the following packages depend on:

• common/librend (name of rendition package)
• html/librend (replacement of common/librend for HTML output)
• latex/librend (replacement of common/librend for LaTeX output)

NOTICE (!!!) the requirement to replace common/librend for HTML and LaTeX output. This requirement is a consequence of the dependency tree: common/libapp2 depends and */libtext depend on it and add to it.

[lueck]

on branch issue-65, commit ae9ac03, we ran into a weired behaviour, where LaTeX is contained in HTML output. This may be an Saxon bug.

[lueck]

We can solve this, by providing extra config files for HTML and LaTeX and may be other output. This would be a breaking change, but the same breaking change would be the end of this improvement anyway.