try_v2 0.4.0

Provides a derive macro for `Try` ([try_trait_v2](https://rust-lang.github.io/rfcs/3058-try-trait-v2.html))
Documentation 
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error: Try can only be derived for an enum
 --> tests/compilation/fail_Union.rs:7:10
  |
7 | #[derive(Try, Try_ConvertResult)]
  |          ^^^
  |
help: not an enum
 --> tests/compilation/fail_Union.rs:9:1
  |
9 | union Union {
  | ^^^^^
  = note: this error originates in the derive macro `Try` (in Nightly builds, run with -Z macro-backtrace for more info)

error: Try can only be derived for an enum
 --> tests/compilation/fail_Union.rs:7:15
  |
7 | #[derive(Try, Try_ConvertResult)]
  |               ^^^^^^^^^^^^^^^^^
  |
help: not an enum
 --> tests/compilation/fail_Union.rs:9:1
  |
9 | union Union {
  | ^^^^^
  = note: this error originates in the derive macro `Try_ConvertResult` (in Nightly builds, run with -Z macro-backtrace for more info)