Initial lesson about python string formatting using the format() method
Removed solutions
Clarified the note about field widths and added an example
Clarified the sentence about the print command output
Fixed typos
Changed line width to 80 characters for the poem formatting and added an explanation
Added machine-readable vs human-readable output, and updated the challenges
Fixed typo
Merge pull request #457 from leyder/python-string-format

New material on python string formatting using the format() method