Make all renderers have the same interfaces

The PDFChart and Chart renderers have been refactored so that they have
the same internal interfaces and public methods.

Closes #15
Fix getting the raw render on the pdf renderer
PEP8 changes
Add some unit tests and travis-ci.org job definition

Add run-tests.sh tool to run the tests. This is just an initial skeleton
of unit testing and there is a lot of work to do, but I think it is a
good base to start with.
Merge pull request #17 from alvarolopez/unit_tests

Add unit tests and fix code to get a clean build
Support for wildcards in condition's values.
Merge pull request #18 from orviz/support_wildcards_in_aggregators

Support wildcards in aggregators
Start using flake8 and hacking
PEP8 changes that prevented the CI to pass
Fix exceptions usage

Some modules were using ConnectorException and others started using
CollectorExeption (that was missing). This commit fixes this.
Fix H302: import only modules
Fix H306: imports not in alphabetical order
Fix F401: imported but unused
Fix H404: docstrings
Fix F841: local variable assined but never used
Merge pull request #19 from alvarolopez/flake8

Use flake8