gopages: fix rendering of doclinks for go 1.19 comments

[phsym]

Hi ! Thanks for this awesome gopages tool. I love it already.

I followed your recent note about go 1.19 and improved formatting, however I realized that doclinks where not rendered at all so I took the chance to try to improve your tool.

To achieve that I did 2 things :

• I upgraded the godoc library to the latest. By the way I also upgraded other libs but maybe I was wrong, just tell me and I'll revert. I haven't updated the go version to 1.19 in go.mod. Not sure if it's needed
• I overloaded the comment_html template func the same way you did for the node_html template func so that it properly rewrite the doclinks. For some reason, unlike node_html links, doclinks are not prefixed by /pkg

I tried it on my codebase (sorry I can't share the full result) but here's a quick example

Without the change:

With the change

With the link properly sending to http://<host>:<port>/pkg/<module>/<package>/#New

DocLinks to doc from other modules or stdlib redirect to pkg.go.dev

[phsym]

Hum ok, maybe I shouldn't have update all dependencies, some may not be go 1.16 compatible anymore, let me try to fix that

[phsym]

Looks like latest golang.org/x/tools requires a version golang.org/x/sys which itself requires unsafe.Slice from stdlib which has been added in go 1.17. Would you be OK to drop go 1.16 compatibility ?

[phsym]

I removed go 1.16 from the github actions ci and it passed

[phsym]

@JohnStarich here's a quick example where it fails before this PR. I'll look at how to make this a test case

// Package example is a dummy package showing how comments doc is rendered.
//
// Here are some random doc links:
//   - Std library: [os.File] [*os.File] [encoding/xml.Encoder]
//   - Std imported: [json.Decoder] [json.Encoder]
//   - Packages: [os] [json] [encoding/xml]
package example

import (
    "encoding/json"
)

// JSONFunc does random stuff with [json.Decoder] & [json.Encoder]
func JSONFunc() {
    json.Marshal("foobar") // Just to import json
}

Not all doc-links are rendered as links, and those which are links to localhost/ which eads to a 404

After PR, links are properly rendered, a linked to pkg.go.dev when they are external dependencies (internal links are linked properly too, will add them to my test case)

[phsym]

I added a test case in gopages/internal/generate/generate_test.go

EDIT: I had to skip this test case when running in go version prior to 1.19

[JohnStarich]

I've released v0.1.20 with your change 🎉