Add functions to check for values near zero
Add include_cols arg to check_near_zero
Add example for check_near_zero
Sort results in check_near_zero by row, then column
Show example of include_cols argument for check_near_zero
Fix bug in check_near_zero: did not return accurate total when specifying include_cols
Add high-level comments in example_check_near_zero
Use %g value format in check_near_zero
Add third column of data that rarely contains values near zero