v0.6.0

• Added a clear_env_var option on the tracer (disables tracing in subprocess).
• Added force_colors option on hunter.actions.VarsPrinter and hunter.actions.CodePrinter.
• Allowed setting the stream to a file name (option on hunter.actions.VarsPrinter and hunter.actions.CodePrinter).
• Bumped up the filename alignment to 40 cols.
• If not merging then self is not kept as a previous tracer anymore. Closes #16.
• Fixed handling in VarsPrinter: properly print eval errors and don't try to show anything if there's an AttributeError. Closes #18.
• Added a stdlib boolean flag (for filtering purposes). Closes #15.
• Fixed broken frames that have "None" for filename or module (so they can still be treated as strings).
• Corrected output files in the install_lib command so that pip can uninstall the pth file. This only works when it's installed with pip (sadly, setup.py install/develop and pip install -e will still leave pth garbage on pip uninstall hunter).