#65: More decoding necessary for Python 3

Also we report now deprecated latin1 encoding (but still allow it).
Any other encoding than UTF8 or latin1 will generate a "null" in
the dependencies field. There might be a better way, so
I filed #67 for that.
#65 Workaround to allow empty arguments in Python3, version bump

This is taken from http://bugs.python.org/issue16308#msg173685
Small improvement to the way the exit is handled

As [suggested](https://github.com/xogeny/impact/commit/cdc5e3b57a4aad9d6dc21344f9c61b1800a815d2#commitcomment-6457061)
by @FND.
#65 Correct replacement of Python 2 StringIO.StringIO

The proper equivalent is now `io.BytesIO`
#69 Report the default (i.e., current) target directory
Add version number to "impact info" (fixes #70)
Avoid inline imports.
#69: Clarify that info on current working dir.
Creating v0.5.9

(might be last version before multi-lib support)