maint: Install ports into /usr/ports/local

* Makefile: New file; install local ports.
* LuaXML/Makefile: Updated accordingly; moreover, fix install bug.
* magit-local/Makefile: New file; remove USE_EMACS from official magit.
* magit-local/distinfo: New file; copy of devel/magit
* magit-local/files/patch-Makefile: Likewise.
* magit-local/pkg-descr: Likewise.
* magit-local/pkg-plist: Likewise.
doc: Update README

* README.md: Likewise.