Also moved the code to SCSS

Signed-off-by: Pedro Ferreira <pedro@dete.st>

Right now, the ToC has an undefined variable i that was an index in the
original ToC code. Since the major rewrite in
4fe062085324c50f2cfa062258559cf31858ef5f it's a recursive function
without this index. The variable `i` was wrongly copied into its current
place from the old code.

This patch replaces the variable `i` with the index of the header
element. Fix the undefined variable problem.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

The ToC generated broken HTML with unclosed `<li>` tags. This got fixed
as well as some minor optimisation and adding list elements for the
subentries so the elements appear in the ToC while scrolling.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

h6 headers are used for tags in CodiMD. So we should ignore them for the
ToC generation.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

This replaces the existing iterative implementation of the ToC
generation with an recursive one.

This also solves the problem of skipped headers which causes wrong
leveling of them.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

Right now the full title of an element is may not shown as the space of
the ToC is limited. With this path it'll be shower on hover and this way
provide more useful information.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

Fixes #637

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>