[Ohrrpgce] SVN: teeemcee/8258 Move global editor SUB declarations to new custom.bi header

[subversion at HamsterRepublic.com]

teeemcee
2016-12-22 19:30:44 -0800 (Thu, 22 Dec 2016)
303
Move global editor SUB declarations to new custom.bi header

Renamed sprite to spriteset_editor, and removed a couple duplicated declarations

This seems to make more sense than defining lots of headers with only
one or two declarations. And customsubs.bi contains only things defined
in customsubs.rbas
---
U   wip/common.rbas
U   wip/custom.bas
A   wip/custom.bi
U   wip/customsubs.rbas
U   wip/drawing.bas
U   wip/subs.rbas