feat(barchart): allow to render charts smaller than 3 lines

Add an internal structure `LabelInfo`, which stores the reserved height
for the labels (0, 1 or 2) and also the state of the labels,
whether they will be shown or not.

The bar values are not shown, if the value width is equal the bar width
and the bar is height is less than one line

fixes #513

Signed-off-by: Ben Fekih, Hichem <hichem.f@live.de>