Made data vs header length mismatch error more verbose
Fix a major problem with parsing TSV files that have empty (that is "") columns at the end of the line. Regular `String#split(regex)` invocation without additional arguments would lose such columns by default, which, it turn, would make parsing of such file completely impossible due to InputError being raised. The solution is to use `String#split(regex, -1)` invocation form, that would honor empty columns at the end of the line properly.

Applied quick 1-liner fix. Added relevant spec and test case file.