Encoding chokes on π and ∞ characters

[SabreCat]

Running encode.py over the current AllSets.json throws errors of the form

UnicodeEncodeError: 'ascii' codec can't encode character [code] in position 27: ordinal not in range(128)

It appears to be hung up on the values "π" and "∞" found in Unstable cards "Just Desserts" and "Infinity Elemental", respectively.

[SilverNexus]

I added Unstable to the list of ignored sets as a workaround. The other Un-Sets are already there. Also had to add HasCon 2017 for mtgjson 4.4.2, since it has ®.

But, in the long run, unicode support would be better.

[nbertagnolli]

I made a pull request you can find here: #29 it fixes this problem : )