Mentioon changed API and ABI in documentation

Changelog

@@ -5,6 +5,8 @@ Changelog for ELPA 2018.11.001.rc1
 - check pointing functionality of elpa objects
 - store/read/resume of autotuning
 - Python interface for ELPA
+- more ELPA functions have an optional error argument (Fortran) or required
+error argument (C) => ABI and API change
 
 
 Changelog for ELPA 2018.05.001

DEPRECATED_FEATURES.md

@@ -11,6 +11,8 @@ been published. All new features of ELPA will only be accesible via this new int
 For ease of transion, the API as defined in release ELPA 2016.11.001 has been frozen in
 and will be still supported for some time, albeit without any new features.
 
+The old, legacy API will be deprecated with the release ELPA 2019.11.001 !
+
 Independent of the freezing in of the old, legacy API from the release 2016.11.001 the
 following listed interfaces will be removed at some time.
 

INSTALL.md

@@ -14,9 +14,9 @@ The release ELPA 2018.11.001 will be the last release, where the legacy API is
 enabled by default (and can be disabled at build time).
 With release ELPA 2019.05.001 the legacy API will be disabled by default, however,
 can be still switched on at build time.
-Most likely with the release ELPA 2019.11.001 the legacy API will be deprecated and
-not supported anymore.
+Most likely with the release ELPA 2019.11.001 the legacy API will be deprecated and not supported anymore.
 
+The release of ELPA 2018.11.001 changes the ABI and API, since more functions have an error argument. In C this error argument is required, in Fortran it is optional.
 
 ## How to install *ELPA* ##
 

README.md

@@ -16,6 +16,7 @@ can be still switched on at build time.
 Most likely with the release ELPA 2019.11.001 the legacy API will be deprecated and
 not supported anymore.
 
+Note that the release ELPA 2018.11.001 introduces error codes to all functions, and thus an ABI and API change was neccessary
 
 [![Build 
 status](https://gitlab.mpcdf.mpg.de/elpa/elpa/badges/master/build.svg)](https://gitlab.mpcdf.mpg.de/elpa/elpa/commits/master)

RELEASE_NOTES

@@ -9,14 +9,22 @@ For detailed information about changes since release ELPA 2018.05 please have a
 - check pointing functionality of elpa objects
 - store/read/resume of autotuning
 - Python interface for ELPA
+- more ELPA functions have an optional error argument (Fortran) or required
+error argument (C) => ABI and API change
 
 ABI change
 ---------------------
 
-Since release 2018.11.001 the ABI has changed.
+Since release 2018.05.001 the ABI has changed.
 
 Any incompatibilities to previous version?
 ---------------------------------------
+For Fortran:
+Break of ABI compatibility, since all functions obtained an optional, integer
+argument of the error code.
+
+For C:
+Break of ABI and API compatibility, since all functions obtained a required int* argument of the error code.
+
+
 
-As mentioned before, the ABI of ELPA was changed; 
-Some new functions (for the generalized eigenvalue problem) have been added