Multi-byte :col_sep support

[jpmckinney]

Ruby's CSV library has a single test for this: test_leading_empty_fields_with_multibyte_col_sep_bug_fix in test_features.rb.

Ragel inlines the when block in an if statement; if the solution requires complex code, we may want to have the block call a function.

However, multi-byte :col_sep is rarely supported in other languages and libraries, so it's possibly unnecessary. At any rate, for csvlint, a multi-byte :col_sep is definitely not a CSV.