Python 3 support

[robstolarz]

I realize this repository is "bugfix only", but the article's future use will be limited if only those with a working python2 interpreter can play along with the examples in the article.

I ran 2to3 on tiddlylisp and then patched up the remaining change by hand. It seems to work:

[rob@Abigail tiddlylisp]$ python3 tiddlylisp.py
tiddlylisp> (/ 4 3)
1.3333333333333333

along with the more interesting features:

tiddlylisp> (define square (lambda (x) (* x x)))
tiddlylisp> (square 7)
49

[StephenTanksley]

You beat me to it, @robstolarz . I was going to work my way through the article and then submit a PR for this myself!

Thank you for this!

[shombando]

@robstolarz thanks for doing this.

I hope @mnielsen will merge this PR since Python 2.7 is out of support and users don't need more reasons to install potential security vulnerabilities on their systems. Especially those who are potentially just getting into programming and might not understand the implications of installing Python 2. Thanks for the great article and creating this repo.

[mnielsen]

Many thanks all! If there are any further changes needed for Python3, let me know - it seems to be fine, but I haven't done a thorough test