Revert "Enum support"

CHANGELOG.md

CMakeLists.txt

README.md

db-schema/cluster.sql

db-schema/schema.sql

db-schema/users.sql

doc/README.md

doc/build.md

doc/configuration.md

doc/db-schema-config.md

doc/install.md

include/hdb++/AbstractDB.h

include/hdb++/HdbClient.h

include/hdb++/HdbppTimescaleDb.hpp

src/AttributeName.cpp

src/AttributeName.hpp

src/AttributeTraits.cpp

src/AttributeTraits.hpp

src/CMakeLists.txt

src/ColumnCache.hpp