'''Tents''' is a puzzle you can find in several places on the web.
Locate the tents in the grid. Each tree is connected to exactly one tent,
found in a horizontally or vertically adjacent square. Tents do not touch
each other, not even diagonally. The numbers outside the grid reveal the
total number of tents in the corresponding row or column.
Clicking in a blank square will place a tent in it.
Pressing 'space' in a blank square will color it green indicating,
that you are sure it isn't a tent.
Clicking button in an occupied square will clear it.