Add pseudo-log10 values for vertical speed and the assorted altitude values.

These will make useful HUD strips easier to implement.
Re-do the altitude strip into a generic "vertical bar" indicator, and add a second one.

This allows an altimeter and vertical speed indicator to be implemented, although any other trackable variable could be done as well.
Merge pull request #18 from MOARdV/master

Finish basic HUD implementation.