Update copyright year

See merge request STJr/SRB2!801

Fix OpenGL "color bug"

See merge request !795

Fix R_CacheRotSprite not working with PNG lumps

See merge request STJr/SRB2!800

Fix seenames not working without a SeenPlayer hook

See merge request STJr/SRB2!799

Clear setrenderneeded after calling VID_CheckRenderer

See merge request STJr/SRB2!793

Fix the issue !678 did, but just don't exit if the file was added twice

See merge request !753

M_Ftrim

See merge request !798

- Use '%f' instead of '%g' to avoid going scientific. Should also fix some
  compiler warnings.
- The trailing zero trimming code is now useful. It started on the terminating
  byte before and wouldn't have done anything with '%g' anyway.
- Use the absolute fractional value to avoid a sign.

"+" command line parameters make sense

See merge request !707

Trim the trailing zeros off floats for cvars

See merge request !716

Local Color Table for GIF movie mode

See merge request !742

Don't freeslot TOL_ twice

See merge request !779

Allow models for skin/sprites with same name

See merge request !767

No more console in menus because codebase sucks xd

See merge request !791

This reverts commit ef3d462e.

Fix object shadow not appearing for mid-joiners

See merge request STJr/SRB2Internal!627

Fix dedicated servers not running gamelogic

See merge request !788

Note to future testers:
Remember to test dedicated servers before merging.
And splitscreen also.