Improve DataType handling

DataTypes such as Integer currently do not get a header generated for them, nor
do they get their subtypes enumerated, and they also get a useless property
header generated.

Use the new isDataType() method throughout the page generation to
handle DataTypes properly.

Fixes #26

Signed-off-by: Dan Scott <dan@coffeecode.net>
Merge pull request #30 from dbs/datatype_handling

CODE: Improve DataType handling