[7.6.0]

[7.6.0]

Bump libatomic_ops version to 7.6.0

* ChangeLog (7.5.0): Bump version (to 7.6.0).
* .travis.yml (addons.coverity_scan.project.version): Likewise.
* README.md: Likewise.
* appveyor.yml (version): Likewise.
* configure.ac (AC_INIT): Likewise.
* src/atomic_ops/ao_version.h (AO_VERSION_MINOR): Likewise.
* ChangeLog (7.6.0, 7.4.6): Add release date.
* README.md: Remove build status indicators for "master" branch.
* src/Makefile.am (LIBATOMIC_OPS_GPL_VER_INFO): Change to 2:1:1
(increment revision number) because libatomic_ops_gpl.so implementation
has been updated (since the last change of the version info).
* src/Makefile.am (LIBATOMIC_OPS_VER_INFO): Change to 2:1:1 (just to
stay aligned with LIBATOMIC_OPS_GPL_VER_INFO).