Enable v0.1 std-trait workaround for additional targets

[josephlr]

Fixes #168

The first commit cleans up how we handle our various helper modules (similar to what we did for v0.2), but does not make any functional changes.

The second commit enables our std::error::Error implementations for windows, target_os = "fuchsia", target_os = "ios". These are the additional windows and unix targets we supported in v0.1.6. We don't enable the workaround for target_arch = "wasm32" as that would be a breaking change (from newer version) for no_std wasm32 targets.

Here is a history of when we've enabled std::error::Error implementations:

• v0.1.0 - v0.1.6:
  • Initially, we enabled the std feature on most targets

  #[cfg(any(
    feature = "std",
    windows, unix,
    target_os = "redox",
    target_arch = "wasm32",
  ))]
  
• v0.1.7 - v0.1.8:
  • We later restricted the implementations to certain unix targets that needed util_libc

  #[cfg(any(
    feature = "std",
    target_os = "android",
    target_os = "dragonfly",
    target_os = "emscripten",
    target_os = "freebsd",
    target_os = "haiku",
    target_os = "illumos",
    target_os = "linux",
    target_os = "macos",
    target_os = "netbsd",
    target_os = "openbsd",
    target_os = "redox",
    target_os = "solaris",
  ))]
  
• v0.1.9 - v0.1.10:
  • We further restricted things to only the "std" feature

  #[cfg(feature = "std")]
  
• v0.1.11 - v0.1.15
  • We rolled back our v0.1.9 changes (as they were a breaking change)

  #[cfg(any(
    feature = "std",
    target_os = "android",
    target_os = "dragonfly",
    target_os = "emscripten",
    target_os = "freebsd",
    target_os = "haiku",
    target_os = "illumos",
    target_os = "linux",
    target_os = "macos",
    target_os = "netbsd",
    target_os = "openbsd",
    target_os = "redox",
    target_os = "solaris",
  ))]
  

[josephlr]

@pie-flavor can you verify that this fixes your problem.

[newpavlov]

Though I do not understand why the UWP build fails in the CI job.

UPD: It looks like for some reason among UWP targets only thumbv7a-uwp-windows-msvc has officially built std, so we may have to use all(windows, not(getrandom_uwp)) which enables std::Error impl. IIRC UWP support was added after the v0.1.8 release, so it will stay backward compatible.