Use configure option yaml path to generate elog-errors.hpp

Add a config variable that can be passed via a recipe to
point the parser to a directory where the error yaml files are.
Rename elog-gen.hpp to elog-errors.hpp, which better matches the
exception error log file names.
Include elog-gen.hpp in elog.hpp so that callers that need to
create and commit error logs only need to include one header file.

Change-Id: Ie3cd65ac761c1f7b2c99c50a2273859283a5ab4b
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/phosphor-logging/elog.hpp b/phosphor-logging/elog.hpp
index 8a35ba5..fe79bdc 100644
--- a/phosphor-logging/elog.hpp
+++ b/phosphor-logging/elog.hpp
@@ -3,6 +3,7 @@
 #include <tuple>
 #include <utility>
 #include <phosphor-logging/log.hpp>
+#include <phosphor-logging/elog-errors.hpp>
 
 namespace phosphor
 {