Added tag pre_speedy_jk for changeset 7fd8eacc738c

State of the project before adding the speed optimizations for j, k, that
actually consist in overriding Sublime Text 3 own linewise motion commands.

The old system present in this revision is less similar to Vim's.
fixes #36, #66, #67 (GH): rewrite j and k as custom commands

This change introduces custom linewise motion commands to better replicate Vim's
behavior.

These changes are experimental. The code is tricky and, although it seems to work fine,
it might prove wrong. In such case, revert to the pre_speedy_jk revision.
Added tag post_speedy_jk for changeset 6c8caeca1744

Changes to make j, k motions faster and more similar to Vim implemented.