version 0.6.0

[wolfgangj]

As soon as 0.5 is done, I will start working on these:

• Improve the documentation generator; it's not very useful currently.
• ncurses bindings; I want at least some basic user interfacing
• Improve evaluator performance; there's a lot that can be done and I'm not satisfied currently.
• Complete testcases for the prelude

[wolfgangj]

make docs will now create HTML documentation in the doc subdir.

[wolfgangj]

The changes I made today have improved the evaluator performance by almost 20%, according to my (simple) benchmarks.