Dependencies; Documentation

* Stripped trailing whitespace from README
* downlodr calls appropriate Python interpreter
* Support virtualenv for python-magic dependency
* Added virtualenv info to README
* Added warning about needing libmagic to README
* Ran README through Pandoc to re-wrap/re-format it
Error-recording; PEP8

* PEP8 adherence
* Keep track of errors encountered in a file in the output directory