used for re-encrypt main ncch partition back into original rom.
idea from CollosalPokemon, and codes from ctrtool & makerom.
tested with MonsterHunter4G and kirameki sweets with these options.

mergerom ..\BFGJ2.3DS --exefs=workdir\exefs.bin --exheader=..\BFGJ_ExHeaderAcce1.bin.out --romfs=..\BFGJ_RomFS1.bin.out
..\mergerom ..\..\hr-kirameki-dec.3ds --exefs=exefs.bin.out --exheader=exheader.bin.out --romfs=romfs.bin.out

all input need extract by ctrtool with -p option, and decrypted by padxorer with proper xorpad files.

you can also use --code=code.bin to merge code into exefs before put them to rom.

TODO:
manual and update partition support.
xorpad support.