Hello GB

This is a port of an NES sprite demo by Damian Yerrick to the Game Boy using RGBDS.

Screenshots

Tested by the author on mGBA 0.7-5026-1a6b47a2 and Game Boy Color with an EverDrive GB X5.

v0.03 2018/05/12

Switch to de facto standard hardware.inc (requested by gbdev Discord members).
makefile: Use target name for rgbfix instead of hardcoding hello.gb.
Hide BG and sprites before game loop to avoid sprite garbage (reported by nitro2k01).
Use palette registers instead of LCDC to hide BG and sprites for GBC friendliness (requested by ISSOtm).
Fade out Nintendo logo while detecting Super Game Boy on DMG.
Add GBC palette approximating that used by nrom-template on NES.

v0.02 2018/03/27

Split into separate files paralleling those of nrom-template.
Use RLA SBC A sign extension idiom (suggested by ISSOtm).
Remove unnecessary and broken OAM clearing.
Add optional zealous memory clearing to satisfy BGB exceptions.
Add doc comments to most subroutines.
lcd_*: Don't push HL so much.
Put global variables and the DMA routine's run address under SECTION control.
Try RSSET/RB to allocate local variables, nearly but not fully eliminating EQU allocation.
Display frame count and initial A, B contents at top.
Change frame count in vblank IRQ, and HALT until it changes.
Explicitly mark MMIO port and local variable accesses as LDH because RGBDS lacks a counterpart to ca65 .importzp. What is this, NESASM? Ref.
Add indentation correction to the build process.
Change padding value to $FF.
makefile: Add BGB as secondary emulator for "make debug".

v0.01 2018/03/22