Titles, descriptions, and default proto package

A couple of slightly different behaviours here, by request:

• Titles will now be added to JSONSchemas. These are either taken from the first comment (where there are more than one), or automatically generated from the proto message name (thanks @mrozycki-tink)
• Newline characters are now stripped from description fields (thanks @jcchavezs)
• Proto3 package is no longer required, and will now default to "package" instead (thanks @amarkevich)