Add spaceships

* Press "F" to switch into a spaceship mode. Right now - one ship per
player.
* Separate lib/ into "player" and "ship": player - humans on foot,
ship - space ships flying around.

Commit references #1.
Spaceships now have rotating target around them

* Target will be used to determine movement and fire direction.
* Hit "h" or "l" to rotate the target.

Commit references #1.
Add acceleration

* Hit "k" to accelerate, "j" to decelerate.

Minor:
* Add some stars to the space map.

Commit references #1.
Minor: all classes inherit from object
Space flight: now in 5 dimensions!

* Add 5D-space handling (player level interaction still utilizes 3
dimensions, which is an intended behaviour).
* Will need to spend quite some time refactoring after the milestone is
complete.

Commit references #1.
Minor: parent for player/ship Level class, PEP-8

Commit references #1.
Generate new space chunk when needed (infinite)

Commit closes #1.
Merge branch 'space-travel' into develop