Add `-o` and `-f` flags

* Add flag to set output file name
* Add flag to force overwrite file
* Change behaviour of matplotlib.py based in this flags

TODO

* tikz.py need some work to using this flags. Waiting the pgfplot
  changes.
Add tikz support to `-o` and `-f`

* Fix some bugs when added `-f`
* Replace all print in tikz.py with incrementation of a str
* For tikz.py if no output file name use stdout
Add legends
Fix -f and don't raise error, only print
Merge branch 'legend' into output

Conflicts:
	perprof/tikz.py
Merge pull request #18 from abelsiqueira/legend

Add legend for tikz