* wip python repl
* reimplement with ptpython repl
* hide extra prompts, general cleanup
* add ptpython to dependencies
* Revert "add ptpython to dependencies"
This reverts commit 1b476e665b.
* inject system dependencies into requirements for run-time install
* write correct requirements.txt contents to disk
* Revert "write correct requirements.txt contents to disk"
This reverts commit 0ba7f0d91d.
* refactor to introduce optional system deps
