add python amalgamate tool

FossilOrigin-Name: 4bab5cee7c6af28e3cbdbf32f5ce4dff7880ad5cdc0020a433b4da8eb876f343

example/amalgamate-python.retro

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+# Amalgamate
+
+The standard RETRO system is built using the Nga VM[1] and an
+image file. The Python implementation consists of several files,
+but it's nice to have a single file copy for easier deployment.
+This tool combines the pieces into a single source file.
+
+Output will be written to stdout.
+
+## Code
+
+Extract and generate the single file source.
+
+~~~
+{{
+  :include-file
+    #6 + s:chop 'vm/nga-python/ s:prepend here swap file:slurp here s:put ; 
+
+  :source:line
+    dup 'from_" s:begins-with?
+    [ include-file ] [ s:put nl ] choose ;
+
+---reveal---
+
+  :amalgamate
+    'vm/nga-python/retro.py [ source:line ] file:for-each-line ;
+}}
+
+amalgamate
+~~~