Enhance “Itemize Lines in Selection”

The command now takes the current tab setting and the indentation level
into account. It also handles description environments more gracefully. Fixes #11.
Remove support for “teTeX” and “gwTeX”

Both of these TeX distributions are unsupported for quite some time now.
Remove whitespace from help document

#ignore
Remove support for “TeXniscope” and “PDFView”

“TeXniscope” and “PDFView” are not under active development any more.