Add explicit TEXT types

[jasononeil]

• Add Text.TinyText, Text.DefaultText, Text.MediumText, Text.LongText
  • Make these correspond with SQL types
  • I'm open to a better suggestion for naming of these types, or promoting them to their own modules etc.
  • Add some unit tests
• Fix node JS mysql driver to correctly handle cases where TEXT columns are returned as a NodeJS Buffer
• Add some stuff to the README
• Accidentally clean up whitespace (sorry about this and the messy commit, I didn't realise VSC had reformatted this when I committed)