Change icon characters if default encoding is not utf-8

Using some platforms which don't use utf-8 as default encoding(especially Windows OSs), verbose icons in the QC result isn't shown and it occurs UnicodeEncodeError.
So I would suggest that non utf-8 environments use ascii strings as icons instead of '\u2600', '\u2601' and '\u2603'.
I added a test script for ordinary unittest module because I inferred from issue #4 that tests would re-write sooner.
Modified: Create icon symbol object of the ArbitraryResultSymbol.
Merge pull request #6 from futoase/changeIcon-proposal

Change icon proposal