Add input marker to set data file relative to sisso.json file name

src/inputs/InputParser.cpp

src/inputs/InputParser.hpp

tests/exec_test/classification/sisso.json

tests/exec_test/default/sisso.json

tests/exec_test/gen_proj/sisso.json

tests/exec_test/log_reg/sisso.json

tests/exec_test/max_corr/sisso.json

tests/exec_test/no_test_data/check_model.py

tests/exec_test/no_test_data/sisso.json

tests/exec_test/param/sisso.json

tests/exec_test/reparam/sisso.json