Fix bug in perprof/main.py

Methods from class MUST have `self` as the first parameter.

Some changes in the class initialization.
Add Pdata class

The Pdata class store the data and provide methods to:

* list solvers
* list problems
* scale computation time
* pretty print the data

NOTE: The pretty print method has a bug for when solver or problem
names are long than 8 chars.
Update README.md to include setup_tools and sudo

Clarify that installing requires setup_tools and root permissions.
Merge pull request #8 from abelsiqueira/readme

Update README.md to include setup_tools and sudo