add instruction "ld hl, sp+nn"

The previous "ld hl, [sp+nn]" is incorrect, but remains for compatibility.
rgbasm: Import undefined BANK() arguments.
Fixed a bug in rgblink regarding the map file generation.

When writing the map file, ROM banks 256-511 were written even if the user never used banks higher than 255. Probably introduced when enabling rgbds to handle 8 MB ROMs.
Merge https://github.com/yenatch/rgbds
Merge branch 'update-legacy-instructions' of https://github.com/yenatch/rgbds
Fixed map file generation. It didn't write some sections' names.

Fixed map file generation. It didn't write some sections' names. It still doesn't write labels in those banks...
Fixed symfile credits output and mapfile section names output.

Fixed symfile credits output and mapfile section names output.
Fixed incorrect placement of symbols in WRAMX[1 to 7].

Fixed incorrect placement of symbols in WRAMX[1 to 7].
Fixed BANK() for WRAMX, VRAM and SRAM.

Fixed BANK() for WRAMX, VRAM and SRAM. getsymbank() returned global bank (0-MAXBANKS from assign.h) instead of just the GB bank number.
Fixed assignation of VRAM, WRAMX and SRAM banks. Fixed symfile.

Fixed assignation of VRAM, WRAMX and SRAM banks (when bank and org are floating). Fixed symfile.
Add .gitignore for repo
Add signature for out_BinaryFileSlice in output.h
Add function definition for strncasecmp for compilation in MinGW.
Define strdup and strncasecmp in separate file.
Add createsybol to symbol.h to get around implicit usage in rpn.c.
Fix dest being unused in float parse function.
Remove unused lines in rgbfix.
Added back lines (commented) just in case they are needed in the future.

Added back lines (commented) just in case they are needed in the future.