warning: struct `OptSourceNoBacktrace` is never constructed
      --> tests/test_option.rs:10:16
       |
    10 |     pub struct OptSourceNoBacktrace {
       |                ^^^^^^^^^^^^^^^^^^^^
       |
       = note: `#[warn(dead_code)]` on by default

    warning: struct `OptSourceAlwaysBacktrace` is never constructed
      --> tests/test_option.rs:17:16
       |
    17 |     pub struct OptSourceAlwaysBacktrace {
       |                ^^^^^^^^^^^^^^^^^^^^^^^^

    warning: struct `NoSourceOptBacktrace` is never constructed
      --> tests/test_option.rs:25:16
       |
    25 |     pub struct NoSourceOptBacktrace {
       |                ^^^^^^^^^^^^^^^^^^^^

    warning: struct `AlwaysSourceOptBacktrace` is never constructed
      --> tests/test_option.rs:32:16
       |
    32 |     pub struct AlwaysSourceOptBacktrace {
       |                ^^^^^^^^^^^^^^^^^^^^^^^^

    warning: struct `OptSourceOptBacktrace` is never constructed
      --> tests/test_option.rs:40:16
       |
    40 |     pub struct OptSourceOptBacktrace {
       |                ^^^^^^^^^^^^^^^^^^^^^

Support `.0.0` nested tuple index

Update documentation of #[from] and #[backtrace] attributes