New commands, changed the behaviour of ch_health, ch_armor

We split override_ols into tas_ols_x and tas_ols_y so that each component can
be set separately.  Each of these new commands takes an argument, while
override_ols did not.  The health and armour are also no longer fixed at the
values set by ch_health and ch_armor respectively as though god mode is
enabled.  We implemented reset_odls to set OLS and DLS to the _current_
position and viewing direction respectively.

In addition, instead of setting the "key value" to "n" after the associated
command is executed, we just assign an empty string to it.  This is to make
our life slightly easier.