Add initial jq-based templating engine

[tianon]

See also docker-library/php#1052 (and linked PRs).

[tianon]

I applied the following change, so I could get a better diff from current to new:

diff --git a/generate-stackbrew-library.sh b/generate-stackbrew-library.sh
index 4c6e0a3..577ba39 100755
--- a/generate-stackbrew-library.sh
+++ b/generate-stackbrew-library.sh
@@ -17,7 +17,7 @@ if [ "$#" -eq 0 ]; then
 fi
 
 # sort version numbers with highest first
-IFS=$'\n'; set -- $(sort -rV <<<"$*"); unset IFS
+#IFS=$'\n'; set -- $(sort -rV <<<"$*"); unset IFS
 
 # get the most recent commit which modified any of "$@"
 fileCommit() {

Diff:

$ diff -u <(bashbrew cat pypy) <(bashbrew cat <(./generate-stackbrew-library.sh))
--- /dev/fd/63	2021-02-08 15:21:05.477809103 -0800
+++ /dev/fd/62	2021-02-08 15:21:05.477809103 -0800
@@ -3,30 +3,30 @@
 
 Tags: 2.7-7.3.3, 2.7-7.3, 2.7-7, 2.7, 2-7.3.3, 2-7.3, 2-7, 2, 2.7-7.3.3-buster, 2.7-7.3-buster, 2.7-7-buster, 2.7-buster, 2-7.3.3-buster, 2-7.3-buster, 2-7-buster, 2-buster
 Architectures: amd64, arm64v8, i386
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 2.7
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 2.7/buster
 
 Tags: 2.7-7.3.3-slim, 2.7-7.3-slim, 2.7-7-slim, 2.7-slim, 2-7.3.3-slim, 2-7.3-slim, 2-7-slim, 2-slim, 2.7-7.3.3-slim-buster, 2.7-7.3-slim-buster, 2.7-7-slim-buster, 2.7-slim-buster, 2-7.3.3-slim-buster, 2-7.3-slim-buster, 2-7-slim-buster, 2-slim-buster
 Architectures: amd64, arm64v8, i386
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 2.7/slim
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 2.7/slim-buster
 
 Tags: 3.6-7.3.3, 3.6-7.3, 3.6-7, 3.6, 3-7.3.3, 3-7.3, 3-7, 3, latest, 3.6-7.3.3-buster, 3.6-7.3-buster, 3.6-7-buster, 3.6-buster, 3-7.3.3-buster, 3-7.3-buster, 3-7-buster, 3-buster, buster
 Architectures: amd64, arm64v8, i386, s390x
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 3.6
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 3.6/buster
 
 Tags: 3.6-7.3.3-slim, 3.6-7.3-slim, 3.6-7-slim, 3.6-slim, 3-7.3.3-slim, 3-7.3-slim, 3-7-slim, 3-slim, slim, 3.6-7.3.3-slim-buster, 3.6-7.3-slim-buster, 3.6-7-slim-buster, 3.6-slim-buster, 3-7.3.3-slim-buster, 3-7.3-slim-buster, 3-7-slim-buster, 3-slim-buster, slim-buster
 Architectures: amd64, arm64v8, i386, s390x
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 3.6/slim
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 3.6/slim-buster
 
 Tags: 3.7-7.3.3, 3.7-7.3, 3.7-7, 3.7, 3.7-7.3.3-buster, 3.7-7.3-buster, 3.7-7-buster, 3.7-buster
 Architectures: amd64, arm64v8, i386, s390x
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 3.7
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 3.7/buster
 
 Tags: 3.7-7.3.3-slim, 3.7-7.3-slim, 3.7-7-slim, 3.7-slim, 3.7-7.3.3-slim-buster, 3.7-7.3-slim-buster, 3.7-7-slim-buster, 3.7-slim-buster
 Architectures: amd64, arm64v8, i386, s390x
-GitCommit: 9625e09996380a78c53a9610915d839035245b57
-Directory: 3.7/slim
+GitCommit: 7f2fc5d31f8fecef999f26d11c5c8f1c95f1d93f
+Directory: 3.7/slim-buster

[tianon]

To be transparent: the impetus for making this conversion was the additional patching we need to introduce from/for #49 (comment), but it generally simplifies (and allows us to add support for multiple Debian releases and potentially Windows in the future).