Support for DeclareFilter.
Updated parser to search for *Declare*

and not the types directly anymore, to handle
DeclareOperationWithCache in ToolsForHomalg correctly.
Fixed bug for empty nodes.

A chapter with only non-empty subsections but no non-empty section was falsely
considered empty.
Fixed a bug with options

A PushOptions in a method which already has options causes
the wrong options to be deleted at the end of the method.
Changed names of comments to start with @Begin...

Also, made chunk standard. Closes #58. Closes #59.