Dependencies like optional and smart_ptr will no longer support C++03
therefore the new minimum language level is C++11, and all the CI jobs
for both C++98 and C++03 have been removed.
Fixed use of the deprecated top level timer class as it was causing
build problems using warnings-as-errors.
Fixed -Wdeprecated-cast in group.hpp.
Fixed -Winvalid-source-encoding in sample_new_features.cpp.
Fixed -Wself-assign-overloaded in format_test2.cpp.
These changes also allow b2 to work properly when executed from
within the format directory.
