Update healthObj.cs

- Renamed to "Health" from "healthObj", capitalisation of type names is inline with other types and "~Obj" is a useless type postfix (of course it's an object).
 - Applying this change will require changing everywhere in the codebase that uses healthObj. Easy for you to do with an IDE,hard for me to do with a text editor! Ideally the file would also be renamed to "Health.cs", but make sure to do this within the IDE (so the .csproj file stays up to date)
 - Changed properties backed by fields into auto properties (just a bit simpler)
 - Moved default values into Start() as property initialisers (could also put them in constructor, depends on Unity specific stuff so that's up to you)
 - Made Health.Set private, it seems like all changes to the "Health" value should be done through "ModHealth(float)" ?
 - Previously ModHealth contained this check:

    if (!_alive && _health >= 200) {
        _alive = true;
    }

Which sets the ship to alive if health is set to be very large. This is pretty bad though, if MaxHealth is 100 then health will *never* be 200 and your respawn logic is broken! Instead I Created a Revive() method which sets health back to MaxHealth *if* the ship is dead.

 - This update was just because I was bored and fancied some easy coding work while I solved a complex problem on Heist. Would you like me to continue doing code reviews like this in my spare time, or to back off and stop fucking with your code?
Merge pull request #5 from martindevans/master

Update healthObj.cs