Inko now supports stable Rust

With the release of Rust 1.28, Inko can now be built using stable Rust, instead of requiring Rust nightly.

This means it's now much easier to install Inko, as stable Rust is typically available in package managers, while nightly Rust usually is not.

When building using Rust stable, various nightly-only features are disabled automatically. If performance is important, we highly recommend using Rust nightly, as this will greatly improve the performance of the garbage collector. The garbage collector uses prefetching as described in the paper "Effective Prefetch for Mark-Sweep Garbage Collection". This can lead up to a 30% performance improvement, compared to disabling the use of prefetching.

Support for Rust stable is available starting with Inko 0.2.0, which can be installed using ienv as follows:

ienv clean
ienv install 0.2.0
ienv default 0.2.0

If you already have 0.1.0 installed, you can remove it as follows:

ienv remove 0.1.0

Whenever possible, ienv will install precompiled packages that have the nightly-only features enabled.

Support for stable Rust was added in the following commits:

• ienv: Support building using stable Rust
• inko: Support building on stable Rust
• inko: Use std::alloc everywhere
• inko: Use std::alloc for immix::block