Set initial row/col position of cursor from command line

[saulpw]

From comment by @wavexx on TabViewer/tabview#152:

I don't see a way to set an initial position for the cursor (in terms of
row/column). I'd recommend to see what we did in tabview/gtabview, which
support the flag:

gtabview +row[:column]

which mimic the traditional seek flag in vi/emacs. Very nice to point
users to specific cells.

This syntax seems reasonable, since it is already supported by vim/emacs/tabview. row should be a 1-based index, and column should allow either a 1-based index or a column name.

[saulpw]

Implemented in develop and will be in v0.98. Initial cursor column can only be numeric right now, as columns for most sources are discovered during async reload, and that's too much to rework at the moment.