testcase for wrong ordering
remove unused variable
fix broken build

add ADD_HEADERS within LibAddPlugin
use ADD_HEADERS for static module (need better approach for such helper
modules)
add add_plugin_helper and way to change -fPIC
Fixed a bug in the compilation variant handling causing the conflict debug option to be always enabled
Fixed a bug causing compilation variants to be installed with the wrong name
add tutorial of compilation variants
do not exclude elektra* functions from being documented
Merge branch 'master' into compilation-variant-fixes
remove unecessary includes

- add_headers already does that
Merge branch 'compilation-variant-fixes'
add cmp benchmark for #38
Add the KEY_END marker on key creation where missing

Add the KEY_END vararg where missing when creating a new key, either
using the C keyNew or the C++ kdb::Key, as done everywhere else.

This fixes crashes in some tests.