Disable lexical block and function debug info caches to improve compilation time while #1694 is unfixed, and fix stack-exhaustion bug in block parent generation.

Closes #1304

Removes a bunch of (eventually) unused arguments. Makes span passing to debuginfo
explicit, instead of relying on the (usually incorrect) spans held in the contexts.

Closes #1439

It's less likely to clash with something than 'neg'.

Issue #1520

rustdocs for f32.rs and f64.rs

It is superceeded by the #[no_core] attribute

Add Inno Setup installer script rather than NSIS

It's not much of a pass, but lets be consistent

Closes #1438

The methods used to implement operators now simply use
the name of the operator itself, except for unary -, which is called
min to not clash with binary -. Index is called [].

Closes #1520

This ensures the lib is not just built, but also copied into the right
lib directory when a rustc binary is used as make target.

Issue #1661