Module Support

In addition to adding a go.mod file, this release also updates the implementation of the %+s and %+v formats to provide semantically equivalent behavior when compiled in either a GOPATH or module based project. All existing tests still pass in both modes. Several cases of using this package in a module aware main program and with stacks that include modules >= v2.0.0 have been manually tested to ensure the results are useful in those cases.

There is one subtle difference in the behavior when using modules. That is, stack frames originating in vendored packages built with the -mod=vendor flag will report their import path as seen in the source code rather than a path in the vendor folder of the main project. Some may consider this an improvement—having paths that match the import path used in the source seems more natural—but opinions may differ here. Also note that the %#s and %#v formats still produce unmodified full paths to the compile time source locations as always.