allow to overwrite the config settings from within a page

This makes it possible to set a different document class or other page
parameters for one page while others still use the default.

It might make sense to restrict which parameters may be overwritten
later.
prefer protected over private declarations

This makes it easier for other plugins to overwrite certain
functionality if needed.

See also https://www.dokuwiki.org/devel:coding_style?&#visibility
introduced a helper plugin to keep data between renderers

This is a first go at #9, even though it does not address globals yet.
This does away with the need for passing data serialized inside the
rendered content.
Merge branch 'protected' into devel

* protected:
  prefer protected over private declarations
Merge branch 'store' into devel

* store:
  introduced a helper plugin to keep data between renderers

Conflicts:
	renderer.php
escape function needs to be available to other plugins
Merge branch 'protected' into devel

* protected:
  escape function needs to be available to other plugins
add removePackage function
Merge branch 'store' into devel

* store:
  add removePackage function
cleanup

this fixes all the errors and warnings shown in IntelliJ Idea for the
renderer class. Other classes still need fixes
some more cleanup
refactor preamble generation

This changes how the Latex preamble is added to the document. Instead of
doing it sequentially and thus writing the preamble right in
document_start(), it is kept in the storage helper and only written at
the very end. The advantage is that syntax plugins can influence the
preamble later on and still have everything in the right order at the
end.

A few more changes are in this commit:

  * utf8x input encoding is now always used and setup in the preamble
    instead of having it in the config. Since DokuWiki always uses
    UTF-8, I don't see why this should be configurable
  * The Latex escape function is moved to the helper class and made
    static for easier reuse in other components of the plugin
  * Packages now have one function to easily print themselves
  * some whitespace padding changes
load additional plugins only if available in tests #16
fixed test for adjusted preamble handling
skip bibhandler test when zotero plugin is not installed #16
Add tests for images in root namespace

Images can also be uploaded into the root namespace of dokuwiki. These
tests address their handling.
Fix rendering images in root namespace

The image can also be in the root namespace, so add a if clause to
handle the case that $src does not contain a ':'.
Merge pull request #1 from micgro42/fiximageroot

Fix images in root namespace
Merge branch 'cosmocode-devel'
Renderer merged.