Usage:
======
Wrap your for loop in an extra scope with a progressbar, like this:
{ // extra scope
Progressbar p(std::cout);
for(i = 0; i < 1000; ++i){
...
p.show(i, 999);
}
} // end extra scope (destructor of Progressbar will be used).
You can give extra information to show in the constructor:
`Progressbar p(stream, "prefix", "Start message", " End message");`
this will look like:
Start message
prefix [===============> ]
End message
You may leave these things empty (`""`).
NOTE: the width of the bar (incl. prefix) is fixed ATM.
NOTE: pass the maximum-value to the function show, not the bound of the for-loop (this way the function also works nicely for floating types)
