* feat: new padding rule for RPX
* fix: documentation on security

Prior to this commit, there was an internal procedure with the merkle
trees to compute empty sub-tree for arbitrary depths.

However, this isn't ideal as this code can be reused in any merkle
implementation that uses RPO as backend.

This commit introduces a structure that will generate these empty
subtrees values.

This commit introduces the re-export of the listed primitives.

They will be used inside Miden to report the security level of the
picked primitive, as well as other functionality.

closes #72

closes #44

Signed-off-by: 0xKanekiKen <100861945+0xKanekiKen@users.noreply.github.com>

Signed-off-by: 0xKanekiKen <100861945+0xKanekiKen@users.noreply.github.com>

Signed-off-by: 0xKanekiKen <100861945+0xKanekiKen@users.noreply.github.com>

See https://github.com/0xPolygonMiden/crypto/pull/29#discussion_r1045108928 where it was suggested.

Signed-off-by: Anjan Roy <hello@itzmeanjan.in>