Render SHA1 links as code blocks

[silverwind]

This changes the rendering of SHA1 hashes to render with <code> blocks, matching GitHub's behaviour. I added a new createCodeLink function and simplified createLink a bit.

Before

After

[codecov-io]

Codecov Report

Merging #6546 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #6546      +/-   ##
==========================================
+ Coverage   40.34%   40.35%   +0.01%     
==========================================
  Files         405      405              
  Lines       54236    54251      +15     
==========================================
+ Hits        21879    21895      +16     
+ Misses      29341    29340       -1     
  Partials     3016     3016

Impacted Files	Coverage Δ
modules/markup/html.go	82.91% <100%> (+0.55%)	⬆️
routers/repo/view.go	41.08% <0%> (-1%)	⬇️
models/repo_list.go	67.89% <0%> (+1.05%)	⬆️
modules/log/event.go	65.98% <0%> (+1.52%)	⬆️

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[zeripath]

Thanks @silverwind your UI work is appreciated greatly