Select asset templates by the final extension only (#114)

compileTemplatesFromDir takes filepath.Ext(rel), with a comment naming
the case it fixes: a directory called users.tmpl whose files are still
normal templates. compileTemplatesFromAsset never got that fix and
still joins everything after the first dot, so for
users.tmpl/index.tmpl it computes .tmpl/index.tmpl.

No configured extension contains a path separator, so the match below
is vacuously false and the template is silently skipped. The same
happens for any multi-dot name such as a.b.tmpl.

Use filepath.Ext here too, so both loaders select the same files and
produce the same template names.

chore: updating repo (#112)

chore: golangci cleanup (#107)

Adding ability to set html/template options

Escape html json (#99)

* use builtin escapehtml for json

* go mod update

* tweak github runner versions

Fix goconst issue, bumped test matrix