Mikrah Megillah And Other Mitzvot Of Purim

The Rambam says in the beginning of the Laws of Megillah that there is one mitzvah מדברי סופרים. And the Rambam titles the Laws as the Laws of Megillah.  What about the other mitzvot of the day?  

The Even Ezra (9:30) indicates that the holiday of Purim is enacted because the people accepted the holiday upon themselves.  This acceptance lasts as the Ramban (Mishpat Hacherem) says that a tzibbur can take upon themselves an acceptance and it is binding upon the future generations as a neder and one of his examples of this idea is Purim.

The Rambam is of the opinion like the Even Ezra that the mitzvot of the holiday are due to the acceptance of Klal Yisrael but mikra megillah is a mitzvah enacted by Chazal.  The proof to this can already be seen from Megillah (2a) where the Gemarah understands that the reading of the Megillah is a takkanah.  That is why the Rambam stresses the mitzvah is that of megillah.  He calls the laws the Laws of Megillah because that was the takkanah of Chazal, כתבוני לדורות (Megillah 7a,) the takkanah that became incorporated as a mitzvah of Chazal is that of mikrah megillah.  The other mitzvot of the day are kept because of the kabbalah of Klal Yisrael (the yesod is in Moadanay Moshe, Rav Avraham Shapira and kuntras את אשר חחלו לעשות uses this yesod to explain many things.)