Adding an esy package

See discussion in #80.

scripts/Makefile.patch

---- Makefile.orig	2019-10-15 22:37:51.000000000 +0200
-+++ Makefile	2019-10-15 22:33:50.000000000 +0200
-@@ -179,7 +179,7 @@
+--- Makefile.orig	2021-10-04 11:15:22.592822933 +0200
++++ Makefile	2021-10-04 11:17:18.684584261 +0200
+@@ -15,6 +15,11 @@
+ SELF := $(lastword $(MAKEFILE_LIST))
+ PARENT := $(firstword $(MAKEFILE_LIST))
+ 
++# In the esy container, $HOME is hidden, but this causes Coq to complain.
++# We thus include a dummy $HOME value.
++HOME ?= $(DESTDIR)
++export HOME
++
+ # This file is generated by coq_makefile and contains many variable
+ # definitions, like the list of .v files or the path to Coq
+ include Makefile.conf
+@@ -211,7 +216,7 @@
  # these flags do NOT contain the libraries, to make them easier to overwrite
  COQFLAGS?=-q $(OTHERFLAGS) $(COQEXTRAFLAGS)
  COQCHKFLAGS?=-silent -o $(COQCHKEXTRAFLAGS)
@@ -9,7 +21,7 @@
  
  COQDOCLIBS?=$(COQLIBS_NOML)
  
-@@ -422,6 +422,9 @@
+@@ -480,6 +485,9 @@
  	$(HIDE)mkdir -p html
  	$(HIDE)$(COQDOC) \
  		-toc $(COQDOCFLAGS) -html $(GAL) $(COQDOCLIBS) -d html $(VFILES)
@@ -19,7 +31,7 @@
  
  mlihtml: $(MLIFILES:.mli=.cmi)
  	$(SHOW)'CAMLDOC -d $@'
-@@ -446,6 +449,10 @@
+@@ -504,6 +512,10 @@
  		-toc $(COQDOCFLAGS) -pdf $(GAL) $(COQDOCLIBS) \
  		-o $@ `$(COQDEP) -sort -suffix .v $(VFILES)`
  
@@ -30,7 +42,7 @@
  # FIXME: not quite right, since the output name is different
  gallinahtml: GAL=-g
  gallinahtml: html
-@@ -585,6 +591,17 @@
+@@ -646,6 +658,17 @@
  	$(HIDE)rm -f $(CMOFILES:%.cmo=%.cmx)
  .PHONY: archclean
  
@@ -45,6 +57,6 @@
 +
 +spell::
 +	./scripts/flag-typos-in-comments.sh `find .  -iname '*.v' ! -path './classic/*'`
-
+ 
  # Compilation rules ###########################################################