Use std::unique_ptr instead of raw pointers.
Change the way the default cubemap is loaded during initialisation.
cache the default cubemap, use stringf for formatting the loading of mod based cubemaps.
Spelling corrections and style renaming etc.
Simplify test.
Fix constness.
Move some stuff around for creating things outside of the draw methods.
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer into skybox
Always init these here.
I surrender, de-const the draw code for Background to fix rendering/OpenGL assert.
Use a cubemap whose faces are 1024x1024 instead of 512x512
add 'repeat' field to KeyboardEvent, set for auto-repeat key events
ignore repeated key events during key binding capture
make KeyBinding fields private; use Enabled() and From*() methods instead
merge left and right modifier keys in KeyBinding code

This means that bindings can only specify a general modifier (CTRL, SHIFT
etc), not a side-specific modifier (LCTRL, RSHIFT etc), and when matching
SDL events, either modifier can be used.
in KeyBinding::Description(), join modifiers with " + "

Translation change: modifier key names should no longer have whitespace
included in the translation; they should also be in title case.
when capturing key bindings, ignore modifiers applied to modifiers

i.e., don't allow "Ctrl + Left Alt" as a binding. Modifiers can still
be applied to non-modifier keys (e.g., "Ctrl + T"), and modifier keys
can still be captured as bindings on their own (e.g., "Right Shift").
keep joystick events connected to BindingCapture after capture has happened
Create a stack of viewports pushed and popped along with the glAttribs.
Merge branch 'master' of https://github.com/pioneerspacesim/pioneer into toasty
Use gas parameters of a hydrogen/helium mixture for gas-giant atmospheres.