Melody Horn 79cf4f6198 Add first-class support for binary crates (#1843)
* autodiscover an exported `main` if possible

this allows for first-class support of binary crates

* wrap `main` to zero out arguments and suppress return value

* add test for bin crate support

* process only the export of the generated main wrapper

* skip most of `export` since only one line of that is needed
2019-11-04 13:34:42 -06:00
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