test doc comments

[Orycterope]

Our documentation code snippets are not compiled, nor tested.

According to an old rust book documentation is only checked for libraries, but not binaries.

We should fix this, as documentation is really important !

[roblabla]

There are actually two bugs here:

• Doc comments for binaries aren't run. This is Doctests don't work in bin targets, non-public items rust-lang/rust#50784 which you mention.
• Doc comments for libraries aren't run either! This is because cross-compiling libraries prevent rustdoc from working: cargo test doesn't compile doc tests for target != host rust-lang/cargo#6460

We should find a way to fix the second one. Ideally, our libs should work on 64-bit targets anyways, so maybe we should try fixing cargo test to work on x86_64-unknown-* along with the current 32-bit target?

[roblabla]

Since #432 we now run the public components' doctests in libraries.

[roblabla]

rust-lang/cargo#6892 got merged, when we next update rust we'll be able to remove the testinner rule.