Add flag to set background

Add flag to inform the RGB color for the background.

Close #76.
Correct pgfplots rgb denominator
Add flag to set page background
Correct bug when background is set and page-background is not
Add YAML support

The YAML header of each file overwrite the options used when calling
perprof-py.

Close #75.
Merge pull request #78 from abelsiqueira/page-background

Add flag to set page background
Update make-examples
Merge pull request #80 from r-gaia-cs/yaml

Add YAML support
Merge branch 'yaml'
Add flag --mintime
Remove trailing whitespaces
Update to work with YAML