Implement decimal and char types

[vcabbage]

Go has no builtin decimal types, would need to determine a reasonable way to represent these without pulling in a 3rd party lib.

Char is UTF-32BE encoded. Ideally this would be converted into a rune.

amqp/decode.go

Lines 658 to 666 in ee6eb7e

	// TODO: implement
	case typeCodeDecimal32:
	return nil, errorNew("decimal32 not implemented")
	case typeCodeDecimal64:
	return nil, errorNew("decimal64 not implemented")
	case typeCodeDecimal128:
	return nil, errorNew("decimal128 not implemented")
	case typeCodeChar:
	return nil, errorNew("char not implemented")