Address [-Wreorder] warning.
Address [-Wsign-compare] warning.
Address [-Wreturn-type] warning.
Address [-Wunused-variable] warning.
Address [-Wunused-value] warning.
Address [cppcheck: stlSize] warning.
Address [cppcheck: postfixOperator] warning.
Address [cppcheck: unreadVariable] warning.
Merge pull request #166 from pal-robotics/fix-warnings

Fix compiler warnings