Update README.md

Fixed some links to point to the renamed documents (they now have an .md extension)
kdberrors.h dependency issue
Merge branch 'master' of github.com:ElektraInitiative/libelektra
move more stuff to kdbos.h

fix ELEKTRA_SENTINEL for swig wrapper
have more informative error messages on python mismatch
split testframework + testcases

move all internal tests to ctest
move framework to tests/cframework
add header files accordingly
do less includes in tests.h
use OBJECTS library for tests (compile it once)
add first ABI test
add more abi tests

add CMakeLists.txt
fix output
move more abi tests
add removed parts of abi tests
use static to get a warning
add broken tests
move broken and buggy tests
remove codegear stuff
move gtest around
check in source plugins
do internal checks on completeness

- check if all plugins are listed in README.md
- and if all are listed in ElektraCache.cmake
- do not allow direct inclusion of kdbos.h
check if functions are double exported
Implement new test strategy

split ABI and other tests
move gtest to tests
fix shadowing, move test to abi tests
improve python2+python3 support

now both python2+python3 bindings can be build at once
use proper python2 for gen tool (fixes problem at arch)
use python2 in python2 binding

Add full cmake commando for debian stable

move Cache to ElektraCache.cmake

(python2 binding is still out of sync with cpp binding)

add_headers where missing