Remove around and between in rubyReserve (#811).

[cconcolato]

Closes #811

[palemieux]

@cconcolato @skynavga What is the use case for "auto"? In particular, how is the author expected to use it in conjunction with values of itts:rubyPosition? Note that the example below does not show any difference between "auto" and "outside".

The four images images/rubyReserve_7A_around.png and images/rubyReserve_8A_between.png need to be removed, right?

[skynavga]

@palemieux addressed #812 (review) in 6ef7ada; I had also been pondering the removal of auto, which did have a subtle difference with outside since it was originally defined in terms of around in the case of more than one line, and around applied before to all but the last line while outside applies after to all but the first line; my conclusion is that we should remove auto since it will be confusing to have both auto and outside due to this subtle difference, and I'm doubtful there is a strong use case for the former around semantics anyway; note that this change upgrades this PR to substantive

[palemieux]

Built at https://rawgit.com/w3c/ttml2/issue-0811-rubyReserve-cleaning-build/index.html

[skynavga]

Merged early per WG resolution.