in activity feed, combine repo path and issue/change prefix into full import path

[dmitshur]

The activity feed on the index page of dmitri.shuralyov.com shows events, such as:

Right now, the following 2 pieces of information are displayed separately:

1. the repository it happened in ("github.com/golang/go" in the screenshot above)
2. the title of the issue or change ("x/build/cmd/coordinator: fails ..." in the screenshot above)

I'm working primarily with Go, and the Go project has a well established convention for including the package as a prefix before the title, e.g., "net/http: add StatusTooEarly (425)". (It makes sites like goissues.org possible.) Additionally, many Go packages have vanity import paths that differ from the repository path that they're contained in, which we can find out relatively easily from go.mod files (see commit https://github.com/shurcooL/events/commit/5bd98dd6544e32f15023245a6225fdbbe4cc9ceb).

It's possible to use that information to compute the full import path of the affected Go package. Displaying that will be more readable and streamlined.

Screenshots

Example 1

For example, instead of seeing the repo and prefix on separate lines:

We can combine them and show:

Example 2

Instead of having to read "proxy:" before seeing that it's the x/net subrepo:

We can combine into a more readable "golang.org/x/net/proxy" import path:

Example 3

Instead of:

We can also include a snippet from the issue description body:

Example 4

This applies to third-party Go packages too. Instead of:

We can show the correct custom import path of that project:

[dmitshur]

This change is implemented and live on dmitri.shuralyov.com now! 🚀

I'm going to take some time before merging the code to master, to make sure everything looks good in production, decide where to place a new package, review and clean it up some more, and then push.