Update how s-values captured

[joethorley]

Use

I(p) - I(1-p)

instead of I(p*2)

[StefanoMezzini]

also add a TRUE/FALSE argument that allows the current behavior but warns users that the functionality will be deprecated in the future and should be avoided

[StefanoMezzini]

after the new PRs and edits, svalue() still returns regular s-values, but directional_information() now returns the directional information log(p) - log(1-p)