This patch adds a context menu to variables in the debugger variable
tree view that has an option to set the value of a variable. An input
box will pop up asking for the new value of the variable, which
is then parsed and used to set the actual variable.
When hovering over a C++ token that we have a man page for, we now show
the man page in a tooltip window.
This feels rather bulky at the moment, but the basic mechanism is quite
neat and just needs a bunch of tuning.
