Make codegen/runtime printing the default

[dougalm]

Unsurprisingly, this changes the quine tests a lot. Here are the main changes:

• ~Floats no longer print with a trailing decimal point. I couldn't find a format string that would print the decimal point without also printing trailing zeros. But I actually think it's an improvement this way. The type can be queried separately so it's redundant for it to also appear in the printed representation. And it's actively distracting when you see the same type printed explicitly in every element of a table. Type uniformity means our textual representations can be more information-dense.~
• Floating point printed precision is a bit different. We're using C g format now rather than whatever Haskell uses.
• Non-Fin tables no longer print with their type. Again, I think that's fine because the type information is redundant. Same story with 0@(Fin 10). We now just print 0.
• No automatic line breaks. I didn't want to implement the layout algorithm from Data.Text.PrettyPrint in the dex AST builder...
• We now print lambda terms as just <function of type : Int -> Float> etc instead of printing their bodies. This is what most languages do anyway. Seeing the lambda explicitly is sometimes useful but there's always :pp for that.
• Some extra parentheses here and there. I'm not implementing precedence-aware printing in the AST builder.
• I decided to print standalone Word8 using hex. Before we printed as the ASCII char itself if it was in the printable range, and some Haskell-defined escape code otherwise. We still want that hack for string literals. But it seems a bit much for standalone Word8.
• unsafe_io gets DCEd in some of the io tests because it's now an argument to show_any but it doesn't produce any non-trivial data. I tweaked the tests but we should revisit this.

[dougalm]

Ok, I added the trailing decimal point. I'll merge once the tests pass.