Fix processing of multiple 'to_name' unicode objects.
Fix processing of multiple 'to_name' unicode objects.

Currently, the method sendgrid.message.Mail.add_to_name only encodes singular
unicode object 'to_name' names to Python str objects. Lists of multiple unicode
objects passed into the aforementioned method does not elicit the same encoding
process. This commit fixes that.

sendgrid/sendgrid-python,sendgrid/sendgrid-python,sendgrid/sendgrid-python,galihmelon/sendgrid-python,thinkingserious/sendgrid-python,blackpioter/sendgrid-python,blackpioter/sendgrid-python,thinkingserious/sendgrid-python,galihmelon/sendgrid-python,blackpioter/sendgrid-python,gabrielkrell/sendgrid-python,galihmelon/sendgrid-python,gabrielkrell/sendgrid-python,gabrielkrell/sendgrid-python