fix(templates/application): Use semantics HTML tags (nav, main, footer)
fix(templates/application): Use semantics HTML tags (nav, main, footer)

Browsers which do not support these tags will fallback to interpreting them as divs.
Ideally, the nav should be a header with a nav inside, but since the header only
contains navigation link, I have omitted it and just used nav.

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io