Merge pull request #8 from ariamania/master

finalized test_add and test_add_value in the test_spectrum.py
Improved documentation.
General functions moved outside of the class.
Merge remote-tracking branch 'oscar'

Conflicts:
	spectraplotpy/importer.py
Dataset tests and lint.
Improved test..
Improved tests.
Merge branch 'master' of git://github.com/lidiabressan/spectraplotpy into lidiabressan-master
Normalizing the content of the files
Starting the documentations.
Adding examples to the README
Merge branch 'docs'
added the test_div() in the test_spectrum.py
added plot() and y_error_plot() in the spectrum.py
Merge branch 'master' of https://github.com/odarbelaeze/spectraplotpy