Simplify array coercion in PGArray
Fix mapping in PGStruct.getAtributes
Comprehensive struct/composite codec testing; all types are now tested as a member of a composite type

• Add a struct unit test for each scalar type automatically
• Fixed numerous type coercion bugs and inconsistencies
• Fixed parsing of structs (text)
• Enhanced parsing of arrays (text)
• Fixed length calculation of multi-dim arrays
• Simplified format support checking for types
• Fixed format support checking of composite types