Added documentation for all ValidForm constant definitions

When adding forms in an intelligent IDE, you now get hints like 'VFORM_TEXT generates a textarea element' etc. Handy dandy.

Signed-off-by: Robin van Baalen <robin@neverwoods.com>
Merge branch 'wip-new-documentation' of https://github.com/neverwoods/validformbuilder into wip-new-documentation