Structure: make it more generic

* changes `orgas` directory to `by_json` (explain what we do: using JSON
    to geneate schema)
* makes Makefile more generic to permit to generate more SVG files in
the future

by_json/filters/libraries

@@ -0,0 +1,6 @@
+.[] | {
+  name,
+  pid,
+  code,
+  organisation: .organisation."$ref"
+}

by_json/filters/organisations

@@ -0,0 +1,5 @@
+.[] | {
+  name,
+  pid,
+  code
+}

by_json/filters/patron_types

@@ -0,0 +1,5 @@
+.[] | {
+  pid,
+  name,
+  organisation: .organisation."$ref"
+}

by_json/filters/users

@@ -0,0 +1,9 @@
+.[] | {
+  email,
+  first_name,
+  last_name,
+  barcode,
+  roles,
+  library: .library."$ref",
+  pt: .patron_type."$ref"
+}