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.
InstallOtherMethod is now handled like InstallMethod. Closes #73
Replace @Chunk by @BeginChunk in manual example
Correct repository address in README. Closes #68
Fixed bug introduced in 96cecb58fe284

Empty chapters and sections should not be printed.
However, there was a bug which caused chapters not to be printed
when only subsections contained text, not a section itself.
Due to the changes, ManItems without description or return value
where not printed anymore.

Closes #80