[8.0.0]

[8.0.0]

Bump gc version to 8.0.0 (experimental release)

* ChangeLog (8.0.0): Set release date.
* Makefile.am (LIBGC_VER_INFO): Increment revision (change version info
of libgc.so to 5:1:4).
* Makefile.am (LIBGCCPP_VER_INFO): Increment current and age (change
version info of libgccpp.so to 5:0:4).
* README.md: Bump major version (set minor and micro to 0).
* configure.ac (AC_INIT): Likewise.
* include/gc_version.h (GC_TMP_VERSION_MAJOR, GC_TMP_VERSION_MINOR,
GC_TMP_VERSION_MICRO): Likewise.
* README.md: Remove build status badges (Travis, AppVeyor, Codecov,
Coveralls, Coverity, LGTM).
* cord/cord.am (LIBCORD_VER_INFO): Increment current and age (change
version info of libcord.so to 5:0:4).