Use comments to split aof.c into sections.
Use comments to split aof.c into sections.

This makes the code more readable, it is still not the case to split the
file itself into three different files, but the logical separation
improves the readability especially since new commits are going to
introduce an additional section.

JackieXie168/redis,JackieXie168/redis,JackieXie168/redis,JackieXie168/redis