Small env fixes: git submodules & python3 (#127)

* Small env fixes: for git submodules & python3

Using `/usr/bin/env python3` is preferred over `/usr/bin/python3`
because it is compatible with virtualenvs, etc. It picks the version of
`python3` currently on the `PATH`, rather than the system-wide default.

For the git submodules, I had two issues:

The ZAPD repo is currently pointing at a commit not on the master
branch, which has to be specifically fetched. Adding `--remote` to the
update command fixes this.

The decomp-permuter has primary branch `main` not `master` like this
repo, so this has to be specified in `.gitmodules` when using `--remote`.

* Rework `git submodule update...` part of Makefile

.gitmodules

@@ -7,6 +7,7 @@
 [submodule "tools/decomp-permuter"]
 	path = tools/decomp-permuter
 	url = https://github.com/simonlindholm/decomp-permuter
+	branch = main
 [submodule "ZAPD"]
 	path = tools/ZAPD
 	url = https://github.com/zeldaret/ZAPD.git

Makefile

@@ -212,7 +212,10 @@ distclean: assetclean clean
 
 ## Extraction step
 setup:
-	git submodule update --init --recursive
+	# Initialize submodules, fetching commit in case it is not on the default branch
+	-git submodule update --init --recursive
+	git submodule foreach --recursive 'git fetch origin $$sha1'
+	git submodule update --recursive
 	python3 -m pip install -r requirements.txt
 	$(MAKE) -C tools
 	./tools/extract_rom.py $(MM_BASEROM)

tools/gen_mips_to_c_context.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import sys

tools/m2ctx.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import sys

tools/overlayhelpers/ichaindis.py

@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import sys